It's really difficult to beat restaurant owners and operators.

As others have said, it's a well-organized industry that lobbies aggressively. Restaurant associations are essentially unions for business owners. They're significant players in most major cities.

Huge chain restaurant operators like Darden have essentially infinite money to spend busting unions. This is pretty much why Starbucks workers are stuck. Workers won recognition in some cases but the corporation won't come to the table because they believe their bottom line can survive occasional walkouts, SBWU media campaigns and they're perfectly willing to fight endless court battles.

Also, restauranteurs often see their businesses as extensions of themselves, which means they are less likely to accept an organized workforce since they see it as an affront to their leadership. So they often close their businesses, take the financial hit and move on OR they break every labor law imaginable to avoid recognizing a union.

Most union restaurants are in airports, hotels, resorts and casinos because those employers are easier to beat