Lots of foods are regulated by the FDA or USDA. Mayo, yoghurt, butter, bread, etc, etc. If you search the FDA or USDA site, you'll find the requirements that must be met for a company to use such terms. That's why Miracle Whip is called a "dressing," in the USA instead of Mayonnaise.
The CFR contains a subsection specifically for frozen pies (though, one of the Trump administrations last acts was to gut this). Lemon bars must contain lemons, per food labeling regulations. Peanuts have a section too.
And yeah, industry lobbyists are largely the creators of legal definitions for foods. If you're a beef producer, you certainly don't want other companies to be able to sell ground up bugs as "ground beef" and undercut your prices or give consumers a bad impression of your product.
I will concede, tacos are not regulated.