The AI isn't that great at money management.  Sometimes it sends a migrator to build the starbase, but spends all its cash before the migrator arrives.  The migrator just sits there until the Vasari AI accumulates 2500 credits (plus the necessary metal and crystal) which might not happen if it's busy making units.  This is more prevelent than with TEC and Advent since their constructors cost more, but the deployment cost is less, so they only need to wait for 1000 credits to build up, which doesn't take that long.

Now, if it never builds starbases even after a very long period of time, that may be an entirely new issue.

Heh...I used that glitch to my benefit once.

I was in a 4player FFA (offline) and teamed up with one AI...eventually.  He started pounding on one of the others, and that would have given him a ton of planets.  With me planning to turn on him I could not have that.  I saw one of the Advent space-tics sitting in the next system in his path and funneled some war-funds to that player.  POOF starbase.