On broadcast and maybe also on cable, the inhibition is what the viewers will accept in character change. I would think that writers would be gung ho to change characters a lot more than they do, but then you're stepping on the toes of the fans who might like Character A just like he/she is, or want change, but in a completely different direction. Guess wrong, and your ratings go in the toilet.
And character change can upset series longevity. For instance, after S4 of Dexter
, I wanted the writers to use the "big event" at the end of that season to propel Dexter into a maniacal tailspin. But the character couldn't plausibly come back from something like that because once you amp the drama, you can't ratchet it back down.
So that development would have signalled that S5 or S6 would have to be the series end. Yet the ratings are strong enough to continue the show indefinitely, which seems to be the plan instead. And to keep the ratings on an even keel, Dex can't change all that much.