Actually, with no viable alternative to compete with, this would be the best time for the wrestlers to try it, Vince doesn't have anyone else, there is no WCW, no territories, there isn't anywhere for him to replace large portions of his roster. It would have been much harder years ago because it would have been tempting for under carders elsewhere to take the chance and jump and to WWE. It's actually just like MBL & NFL, there are no other leagues doing what you do in the US and the quality of players you might be able to bring in would be so low the product would suffer and you would lose money (You do remember the 1987 Replacement NFL games correct).
There's no place for these guys to go. They have no cards to play. It would be idiotic to walk out. And the NFLPA which was once the strongest of all sports unions is actually weaker than it's ever been. Their last collective bargaining agreement was heavily lopsided in favor of ownership. Why? Because the players know there's no USFL out there anymore.