Because those moves tend to be better than uproot which is tower only.  Also what infinite vengeance said.

I'm not even sure Spit would be on the list of OP skills early game.

There's a specific skill that only exists in the early game that deals with how you harrass and defend against harrassment in the first few levels, when you have low health regen and cannot afford too many consumables. This plays a lot like DOTA if you are familiar.

UB is certainly a good early game harrasser, but there are a few ways to prevent that:

1. Many characters can harrass back. Torchbearer, for example, can hit from long range with Rain of Ice or Fireball, plus if he does get spat on, he might as well throw a few auto attacks out at range, since UB only has a single ranged ability. Spit is better than Rain of Ice (ONLY considering early game harrassment, both are amazing abilities on the whole), but the extra range on your attacks makes your non-ability harrassment better. It only takes a few hits to equal the damage of a Spit, and that doesn't even consider your special abilities.

2. Good early game item selection and favor item selection is important. I like to grab Scaled Helm + Banded Armor myself, but potions can also be good. For favor items, there are a variety of defensive picks, like

a. Blood of the Fallen: 800 HP and more health regen makes you hard to kill.

b. Wings of the Seraphim is a full heal for every ally in your lane early game, and is still pretty good late game.

c. Sometimes the best defense is a good offense. I prefer offensive items, as I bet on being able to hurt enemies more than they can hurt me. It depends on your playstyle.

3. Love your towers. This is hugely important. Low level DGs cannot get too close to your towers, so if you are near them, or better yet, behind them, you cannot be meaningfully harmed. Remember you do not have to do any damage at all to get experience from reinforcement kills, and the gold isn't so large that it will swing games.

4. Work together. Sedna and Queen of Thorns are very hard to kill, and more importantly, can make everyone near them very hard to kill. A Bramble Shield costs less mana than many attacks, but stops more damage. A level 2 Sedna reduces Spit damage by 20% just by standing next to you (if she takes the heal aura).

These are just a few comments.

Everyone has access to Restorative Scroll, I'd suggest buying some for $250.

http://www.scarylogic.com/demigod/items.php

As Xinoxlx has pointed out, many demigods have abilities that also counter the damage over time.

UB has some of the same issues as Erebus in that mostly new players have problems with which is they DIE far too much to both demigods.

Erebus, bite and movement speed reduction means you have to really... really keep your distance and run early! 

Same goes with UB, you need to have Restorative Scrolls and health potions ready to counter the health loss and just like Erebus if you don't have those tools you need to run super early so that you don't give kills away.

http://www.gamereplays.org/demigod/portals.php?show=page&name=TotW-Demigod-Tip-Unclean-Beast-UB-Spit&home

UB is not OP.....
Since its DoT, not instant. Any Demigod can do that damage over the time that spit can. TB Can cast fireball, run, cast fireball and deal 2k damage easily. Does that make him OP?

Your never forced to take Symbol of Purity. Its just if your going to complain or think that UB's spit is OP and struggle with it, and your not SIX out of the Eight Demigods that can deal with it (TB or Regulus) then you should take it.

@ DalzK

Oops, my bad.  For some reason I thought it worked on Demigod's as well, DOH.  Well in that case for generals it can help protect there minons from effects, but yes that makes this item pretty much worthless.

Well damn, guess you learn something new every day!

Spit does have a lot of counters.

Also... I can spit pretty far so I would imagine a demigod would be better at spitting than myself...

It's a contest, will they get towers or spit nerfed next?

If your a competent Rook player and can use Hammer Slam and Bolder Roll effectively you can make the UB have a very hard if not impossible time killing you. Mid-game if you can kill the UB over and over and refuse him buying items then he will get much weaker as the game progresses as you get more powerful.

IF you let the UB kill you and farm gold though, lategame the UB is very, very hard if not impossible to defeat.

(edit: never mind -- 2v1 = death anyway)

i think everyone is missing the most crucial point regarding balance adjustments. you need to be thinking about whether or not the performance of the ability is within bounds of what other DGs have access to. Bite was nerfed because its mana efficiency was off the charts. so they raised its mana cost (alot) and lowered its damage (a little). now its back in bounds. 

so compare Spit to other similar direct damage abilities, and while allowing for some range of variation of performance find a way to determine if its within bounds or not. 

try something simple like a comparison to other abilities that deal only damage and have a similar cooldown. 

Fireball (http://demigod.wikia.com/wiki/Fireball)

cooldown: 7 sec, cast time: 1 sec, max range: 20, duration: instantaneous

damage: 300/525/850/1050

mana: 300/380/460/540

efficiency (damage/mana): 1 / 1.38 / 1.85 / 1.94

total max single target DPS (damage/cooldown) : 42 / 75 / 121 / 150

aggregate potency rating (DPS*efficiency): 42 / 103.5 / 223.85 / 291

Venom Spit (http://demigod.wikia.com/wiki/Venom_Spit)

cooldown: 7 sec, cast time: 0.3 sec, max range: 15, duration: 10 seconds

total damage (initial + DoT): 500/800/1150/1500

mana: 500/650/800/950

efficiency(damage/mana): 1 / 1.23 / 1.43 / 1.58

total max single target DPS (damage/duration): 50 / 80 / 115 / 150

aggregate potency rating (DPS*efficiency): 50 / 98.4 / 164.45 / 237

notes:

its possible to have venom spit on more than one target at a time as its cooldown is shorter than its duration. this is a small advantage for Venom Spit but was not considered for this analysis because it is not a very common situation and is kinda outside of the context anyway. if you want to start comparing multi target damage, you'll find that Spit is probably the worst ability in the game for that, in terms of efficiency. 

there are still minor differences between the two skills so my strictly numerical comparison doesn't capture everything.

...however I think the numbers say quite alot. Fireball is actually a noticeably better damage ability than Spit in alot of ways. 

when i did this same comparison between Bite and its nearest similar ability, Oak's Penitence, i found that Bite was like 2 or 3 times as efficient as Penitence despite having similar effects. it was obviously out of line. in the case of Spit and Fireball its obvious that the abilities are close, clearly within acceptable range of variation, and that Fireball is actually slightly better. 

my conclusion from this is that Spit should not be nerfed. 

If you're a squishy demigod and UB is close enough to use spit on you, you deserve to die.

Could do with lowering the range a bit, but otherwise it's fine in my opinion.