Bowser decided he needed some help around the joint. People to flip burgers, people to make the Koopa fries, and someone to remind his dumb self to remember which side of the sign says "open", and which side says "closed."
Bowser went back to his castle one night after somehow getting through the full day's worth of customers. Bowser worked through the night building several mecha koopas.
When morning came, Bowser was very tired. He brought his Mecha Koopas to the restaurant and activated them all. With all those Mechas making the food and serving the drinks, those taking orders and such, Bowser decided to leave the place in the hands of the Mechakoopas while he set out to try and subject the Mushroom Kindom citizens to go to his restaurant.
The master of multiplayer Mario games: You''re looking at him right now!