The coaches did. Not only did they accept them, they implemented them.
"Invalid contracts cannot be made valid simply because you adhere to some of the conditions"
Some? Try all. Or maybe you could tell me which conditions were not adhered to from Day 1?
That said, perhaps the commissioner's conditions were indeed invalid. The time to challenge them, however, was at the beginning of the season, not the final game. Since the coaches honored those conditions throughout the season, the commissioner had a reasonable expectation that those conditions would be honored in the game he was unable to attend.
Nope. You cannot have a reasonable expectation of unreasonable demands.