It's known fact that almost everyone's goal is to make their comics into movie(s) or TV series. If Mike is on board, it's for couple of resounds: work recognition(which I can approve) and money(which I would choose too). No more no less. I personally wouldn't set my house on fire if there will be HB3. Mike didn't had much saying in secound movie to begin with. As he stated many times in conventions, especially about secound movie, that it belongs to Del Toro and he had very little to do with the story and production. And I liked HB1 for couple of resounds, but secound movie made me embarrassed with elements and direction it went. The fact that movie Liz is pregnant with Hellboy babies, brrrrr.