Disney used to have a rule not to do more the 2 seasons of any given show so they didn't let any one show get popular enough for writers or actors to negotiate better pay.

Also because they had very rigid TV scheduling which is why it is such an exact number.

It's called the 65 episode rule. I think they stopped it but still have a pretty high bar for what gets to be extended. And the mouse holds to all its IP for the rest of time even if they don't plan to do anything with it.

Marvel before Disney owned hundreds of random super heros non-nerds have never heard of.

I think they before Disney they used to be open to selling any random ones but stopped after the success of Guardians of the Galaxy which had pretty obscure super heroes. So they have vast vaults to pull out characters for blockbusters.