Last season PG averaged 22/5/3, 41% from 3, 90% from the line, 57% effective FG pct. He's still one of the best players in the NBA. He fits exactly what the Sixers need, someone who can spread the floor (and is willing to do so) and is an excellent defender. Porzingis hadn't won anything before last year either, and now he has a ring.
The Sixers have needed an elite wing since they traded Butler. PG is easily the best one available, and he would cost them nothing but cap space. They don't need him to be THE guy, they just need him to do the things that he's good at, and that he's been doing his entire career. It will cost a lot of cap space but the Sixers window to win a title with Embiid as the centerpiece is getting smaller every year. It's pretty much a no-brainer for Morey.