Also, he's probably happy that he doesn't have to sing Eagle Fly Free (and be criticized for it) anymore. Which is basically all the thanks he gets for having, as you said, helped to recover Helloween which were basically done in 1993 and helming them to 20 years of sometimes good, sometimes great albums, to which he provided his songwriting skills, while being one of the very best frontmen of the entire genre. He was never afraid of the reunion (I remember a video interview of some years ago where he said that he wouldn't mind to let Kiske join in the encore and be backstage for 3 songs or stuff like that) and, as the true "master of the house" since 1994, welcomed Kiske back without ego or insecurities and eased him back into the fold.
He also looks like being actually a very cool and chill dude, maybe it helps that he lives on Tenerife. Think of it, the dude lives all the time on an island. He has his studio there, so when it's time to write an album, he works from home. And then whe he leaves home, he does it to tour the world and have concerts with screaming fans all around. No wonder he always seem happy and uplifted.