It is my opinion that CM Punk's UFC stint completely broke him mentally. In the WWE he always had a massive ego, but he was never going around threatening to beat people up. I think getting embarrassed in front of the entire world in the UFC bruised his ego so bad that he's now trying to overcompensate with the "take this outside" bullshit.

Or all the WWE wrestlers were bigger than him and he knew better to even try, but armchair psychoanalysis is more fun.