I think he sort of morphed into that because it helped his career. I'm not 100% convinced that Skip or Stephen A are the same at a dinner party as they are on air.
Honestly, the entire job of on air talent is to get a reaction. If people are indifferent to what they're saying, most don't last. Mike and Mike get away with being non-controversial because they're first on air. They can report the overnight news. The shows that follow them have always been a little more edgy. Blame Howard Stern.