Wentz is projected to be ready by the beginning of the season but may not. Foles is also a hero in Philly now. He'll be VERY cheap to keep as a backup after 2018, unless they feel obligated to do right by him and give him a chance to start somewhere. Even then, they aren't going to lower their price just because fewer team are bidding. The alternative to not trading him is potentially having the best backup in the league, for a guy coming off a torn ACL, and both combine for a very reasonable QB salary cap number.
Some people have the wrong narrative. Foles is absolutely available to anyone who meets Philly's price. That does not mean Philly NEEDs to trade him.