The fact is there's no incentive to leave. The only cost to staying in the league is the credit that is being used as a placeholder in the league. If at some point he wanted to renew another team, but didn't have any available credits or $25 to spare, then it costs him to sit there. But at this point, why not wait and see?
For markets to work efficiently, however, failing businesses need to be allow to fail and close. The same goes for HBD worlds. The big difference is that there are no ongoing operating costs to keep your failing world from dying. Invest $25 and you can keep it going forever.
Of all the solutions I've heard, the one that makes the most sense to me is to allow the sim to run open teams. It's a win-win all around. WIS gets to actually cash in on the teams that have paid for that season, owners get to actually play the game, and WIS gets closer to having the committed owners renew. After a certain period of time (say 4 weeks), let the sim take over available teams.