The trouble is, even if they do get sued, they won't tone down their ads or increase the quality of their food, they'll just put more disclaimer text in small print below the ad
"fried chicken sandwich" outside America vs "chicken burger" seems to depend on whether you use a burger bun or not, at least that's my observation. The secondary observation is that for dietary reasons a lot of places don't primarily think of burgers as exclusively beef or pork so the swap/substitution is already well underway for what makes a burger patty/filling.
(ETA: so by the time our English settled on understanding a burger is a sandwich using burger buns, then just about anything in the middle can sub for a meat patty)