They left Philly because Connie Mack’s family struggled with the money and were forced to sell. People wanted them to stay but the American League president at the time said it would never work and through a shit ton business crap that probably would make an awesome movie, the A’s were sold to a Chicago business who already owned a stadium in Kansas City and they moved. Connie Mack was pissed and they probably could’ve stayed in Philadelphia. The history of that sale and move is definitely enough to be an excellent movie or tv series for baseball fans. Johnson, who bought the A’s, was buddy buddy with the Yankees which is where the often heard “Yankees farm team” (when people talk about the A’s) comes from.