>>22971983
It's not tariffs. As >>22971987 hinted at the main costs of running a food place are now so close for fast food and casual restaurants that the cheap fast food niche is gone. Labor, real estate, regulatory compliance and taxes. Once you pay enough to be able to open your shop, the quality of food you're serving doesn't change your costs that much.

There's two things fast food can do:
1. coast on momentum, branding, and competitors' mistakes
2. come up with a new business model that actually reduces costs.
McDonalds is the reigning champion of #1, and #2 is being dominated by individual local guys.