Stars are designed, like upvotes and close votes, in that, they should be used sparingly to determine the worth of questions, or in this case, chat posts.
Whilst in The 2nd Monitor, starwalls and pointless starring are somewhat commonplace, other chat rooms don't take so kindly to over starring things.
By limiting stars you can avoid situations like this.
With unlimited stars, you could potentially star everything and then the whole idea of starring to highlight interesting content would become pointless.
