OOTP doesn't make it particularly easy to run or be in online leagues, and the world of multi-player environments has changed considerably to make those issues even bigger.
But IMO leagues live and die based on their culture and what the GMs bring to them just as much or more than the game itself. It's an interesting balance. Commish and GMs vs. Gameplay. Every league is a little different. My guess is that there's a natural progression, and if a league can last (say) two real years, it can last a very long time with the right back office support.
But that's a lot of work.
Very good online commissioners are worth their weight in fake gold.