Yeah - money. I think it simply isn't worth the time and money for a team to go after these guys. I mean, how often is it that a guy holds out of the regular season? Not often. An argument could be made that those are the only times that a team truly suffers any loss (games). Moreover, we agree that specific performance is not an option, so the thing actually sought, e.g. Galloway on the field on gameday, can't be achieved. The available alternatives are few, so even if they hire someone else it isn't like they're getting another Galloway. The "cover" of signing another player will likely cost the team far less than a player good enough to hold out, and therefore the team probably has no real damages. So why spend the money and time in court? It would gum up the works for the league, increase owner overhead, etc. Just trade the guy (like GB did with McKenzie), let him be someone else's problem, do what you can in-season, and find an alternative next off-season.