He fell out of the rotation in Philadelphia when they were a contender less than a year ago and he plays 24 mpg off the bench for a team that's one of the bottom five in the NBA. Although he did get an offer sheet from Dallas, it's not like he was a hot property as a free agent.
Philly gave him up for basically a 2029 second rounder... (assuming Hart is worth a 1st rounder from NY, the 2nd they gave up and received were a wash, and McDaniels was worthless). It seems crazy to think he'd be worth more now than he was then, especially a first rounder and second rounder more, but I guess anything is possible.