It's very hard to unionize. I ran a pizzaria for about 10 years and was the owner operator it for another 5. The employment length of tipped employees typically is around 6 months. With people coming and going so quickly, it's hard to develop the bonds that allow such organizing.

For positions filled people that are completely replaceable in hours, including finding and training them?

The answer might be obvious to you, but it is not to me. That's why I asked..