1. Mike, Kevin, and Bill could not come up with anything funnier than what was happening on screen.
2. The actors were really committed, like they were not bad performances it's just what they were doing was shit.
3. No one involved with the script had ever heard, played, or been in the same area code of a super mario game. It seems like they grafted third hand accounts of gameplay onto a YA script that was collecting dust.
According to this documentary, there was a serious breakdown in communication between the directors, actors and producers and the screenplay was rewritten multiple times, even during filming.