Yup, but still before making Monkey Ball, he's working on Virtua Racing (his first title as a designer) and Daytona USA (as Director).
Sega of Japan CEO at the time complained that games became too expensive to make, and Nagoshi was kinda unhappy hearing it.
As his type of protest, he developed a very simple and inexpensive game that just needed a lever to control with no buttons, just to prove that it was possible. That game was Super Monkey Ball.
If that's the case, I can see why he's gone off SMB series.
Nagoshi: I'm trying my damned best here and you're saying they're too expensive to make! Well here! Here's a game about a stupid little monkey inside a ball. Push level, pbbbt! There!
CEO: Why... this is perfect!
Nagoshi: Whut? you're not suppose to like it.
CEO: Let's make a franchise out of this!
SMB fans: We love it!
Nagoshi: STOP LOVING THIS UNIRONICALLY!