Maybe because Jericho honestly feels as though he still has enough star power to put people over. Maybe he wanted to do so much more but was handcuffed by Vinnie Mac. Nobody knows what's going on with Chris Jericho better than Chris Irvine. Also, I think the main reason Y2J keeps coming back is because he truly loves performing, whether it be in a ring or in a band.
I think this pretty much sums it up for the most part. Jericho loves wrestling and while he could always go to any other company in the world to wrestle, he knows that he can make a lot of money for the limited amount he'll be working. He loves it, but he's also being smart about it. If it was all about the money, or even mostly about the money, Jericho probably would've hung up his boots a long time ago.
Jericho has a reputation of being one of the most unselfish guys in the locker room. When he was a young guy in WCW, he was essentially restricted to being a mid-card comedy act despite the fact that he was great inside the ring and could very much hold his own on the mic with anyone in WCW. However, Jericho wasn't one of Bischoff's boys. Because Jericho had such a tough time in WCW because the powers that be wouldn't give the guy a shot, Jericho himself is someone who enjoys putting over younger talent, he's attained legendary status in his career, can still deliver in the ring & on the mic and programs with Jericho can benefit up & coming guys.
MAYBE that generosity has resulted in him not being as big of a star as he could have been, but I doubt it. Even if it has, Jericho won't complain and he's not got all that much to complain about. He's made a lot of money, he's worth somewhere around $20 million when last I heard, he's still virile, he's in great shape and can still deliver the goods when most guys his age, including pro wrestlers, have long since started going downhill.
Also, Jericho's only back for a few months at a time. As a result, he's not gonna be winning any championships nor is he gonna be viewed as a serious contender for championships. Jericho turns 44 in about 6 weeks or so, which means he's not gonna be the future of the company. He's still got enough juice as a wrestler and star power to possibly help get younger talent over while making a nice chunk of change. He obviously feels that it's worth his time and that he has enough to offer.