The thing that bugs me a lot is that Teen Titans had a storyboard, and a pretty decent one. it almost got away with another season, but Cartoon Network decided not to go through with it (It also sounded like a cool season, but whatever).
That being said, it was cancelled. Afterwards, Cartoon Network did actually make a few shorts that were in a more cartoony style, but they were a few minutes long and weren't made into a whole show (they also still made sense). So the show wasn't really running too stale. With the extra season or without, that was pretty much the perfect amount of time for a series to last. Together with the shorts, it was fine.
It became a "beat a dead horse" situation when years later Teen Titans Go came out and destroyed pretty much all of the character personalities and used "idiot humor."