I think Jon makes a key point, too many owners abandon one team to take over a better one somewhere else, or start a new one.

One option might be to have leagues that are not perpetual. In other words 160 game launch leagues, both RealTime and Trad, for owners that want to put together a new team each year.

I also think if you paid by the season some owners make take the longer view and not be as quick to dump when the team does badly. It also might stop some of the more "off the cuff" drops that happen when a trade is overturned, or the stats are particularly out of whack early, or a person is having a busy time and can't focus on the team for a bit. These all cause frustration and can lead to dropping a team when really the owner might just need to take a few months away from the the team.