The running joke is that Frank Gore is one of the greatest Philadelphia free agent signings ever. It’s a stupid joke because the guy never actually played a game here. He agreed to come to Philly, then decided to sign with Indy instead, and explained why on Rob Maaddi’s podcast:

Gore was on to something, eh? He knew Nick Foles was gonna be a Super Bowl winner, long before the rest of us did. Frank didn’t wanna mess around here with Sam Bradford. He saw Chip Kelly wheeling and dealing before he was canned by the Birds.

There’s your explanation, from the legendary Eagles running back.