I gave up a team in 63 that were perennial poor, never made playoffs. I took them from 1-15 to 13-3 in the space of one season. Not gloating, but I gave them up because I had no desire for a "long term" project. I also gave up a pretty good NYJ team (4-1) in the parody league due to wanting to focus on my other teams.
Nothing wrong whatsoever in quitting a team/league....dismantling them (intentionally making them weaker) and then quitting should result in a name & shame in my opinion.