Or maybe it was the 40th anniversary and they brought back as many people as they could and Hayden realized he liked it and could also make a ton of money selling pictures and autographs.
Hayden probably wouldn’t have made the decision himself, due to the harassment he received for his performance as Anakin. It wasn’t his fault, but fans still bullied him, just like Jake Lloyd. Thankfully Hayden didn’t go through an emotional breakdown like Jake did, but I think he was still hesitant to show up at another Star Wars event prior to Celebration 2017 in Orlando.
Yes I wouldn’t be surprised if he skipped prior celebrations because of the PT hate. But I’m sure those fears went away completely at the 2017 celebration and that’s why he’s back (i.e. not because of IX).