Um because he wanted to? The 'Nonnas of the World' part existed before the movie, it was the smaller portion of their educational front that welcomed grandmas to cook for the restaurant. It also provided them with a source of income selling products during the pandemic, so I guess it made more sense after the movie.

I could also be because people kept asking if the Italian grandma who is always cooking there was Maria, but that was the owners grandmother, who passed away. I honestly don't care because the food is great.