I think we have two classes of "fast food" now. The higher class places like Five Guys, Poke Bros, Panera are going to cost you more, and you're not going to go there every day (or even every week), but they're pretty damned good.
The OG fast food places - McDonald's, Burger King, Wendy's, Hardee's/Carl's Jr., Arby's, Taco Bell - they're just not good enough to command the higher prices that the new class of fast food can. Not to mention that the quality of all of those chains has declined dramatically in the last decade. Obvious drop in quality plus increase in price, people notice that.