He was never coming back on Sunday Night Football, against the undefended biggest Cowboys rival, and with the team 4-0 without him. There would just be too much pressure for him to play well and too much risk that he doesn't against the Eagles on national TV. Then you'd have to hear "but Cooper Rush led the team to 4-0 and now Dak looks horrible and we lost"!
He'd much prefer Rush look bad and we lose (So far it's looking good for Dak there), so he can come back against the worst defense in the NFL next week instead.