Maybe they are experimenting with the option of expanding your city into a forest / river / coast to add the production or food bonus.
Am not really sure if it would be good to allow construction of those 2 improvements with snaking, they would sort of kill a bit of decision making when settling a city, and only factor to take in consideration would remain the number of essences available per tile.
As it is now, I can go for a no essence 2/4/0 or 2/5/0 tile that is near a river or forest, or 5/2/1 near a forest etc. But if I can just sneak to the forest or river, then obviously I'll go for highest essence tile.
On the other hand it would make sense to be able to take advantage of a nearby river / forest if my city borders connect to it.
How to balance this out?