The big difference is this game is coached by NFL coaches, has scouts from each team and multiple head coaches coming to watch practice and speak with players. It's the NFL Combine in pads. They are playing for the reason they skipped the bowl game; to make themselves ready for the NFL.
But they do all same in bowl games...except coaching....but get ur drift..
Usually the players in the Sr Bowl are those that think they need more time in front of the scouts, to try and improve their stock.