No thanks on the chatroom.
As for his reasons, I think he's a horny, old man looking to rob the cradle something fierce. Meanwhile, her dad's country (she is a Princess, right?) has got a hell of a deficit, so they can't afford a knight in shining armor or any such thing and would be really embarassed to marry her off to a giant snapping turtle, despite the fact that he's rich as all get out. So, they figure the only way to get her back is to offer up the smallest pittance possible and hope for the best. Well, plumbers aren't paid much in that realm (damn non-union labor) and so Mario figures he can make some easy cash. Hell, his brother sometimes jumps in for a cut of the profits. They go and do their thing, but Bowser is the Custer of defensive logisitcs and the Princess just plays along long enough to get her pink, little ass home safely. Of course, the plumbers aren't hit men, so they always do a half-ass job. I mean, do you really think a guy who works with flanges for a living knows dick about making sure somebody stays six feet under? So, Bowser keeps doing his thing, the king keeps bailing out... I mean, overspending on other things, and Mario keeps hoping to whatever God the Japanese gave him that he can squeeze a kiss out of blondie.