I might piss off some fans here, but Philly isn't/wasn't just Blue Collar it was white and Catholic. The Phillies were late to add black players to the team and so were the Eagles. Not too many Blacks in Hockey!
The 76'ers were black, and while Phila. had a large black population, they had other concerns than spending money to watch basketball.
The Big 5 and the feeder parochial schools where also white, Catholic institutions, St. Joe, Villanova, LaSalle.
When the Sixers won their first title, the fan favorite wasn't Wilt or Hal Greer, it was sixth man Billy Cunningham, white and Catholic, I think out of Brooklyn by way of N. Carolina.
As the City grew the whites moved out to the suburbs and became Hockey fans and forgot about their basketball roots. Given the history, and how fans are made the way they are by the families they grew up in. Phila. sports fans like the Eagles and Phillies first, then the Flyers and then the Sixers.
I always liked basketball better, but I'm in the minority. I don't know too many Sixers fans here. My friends like the Eagles, won't even spend their money on a baseball game. My nephew like Basketball, but he's a LeBron fan.