I think a lot has to do with how much work you put into your league.
When you spend dozens of hours on logos, jerseys and caps, maybe even on schedules you definitely think twice before deleting your league.
On the other hand I also start to lose interest in my historical leagues pretty soon.
It's quite simple - you normally take your favorite team, but once you start to dominate your league year after year and all it comes down to is if you win the World Series or not, things start to get boring.
So in my case - I have a hard time to keep up interest in my historical league, but I simply can't get enough of my fictional leagues
