Because when its good, its so fucking good. They spend literal millions developing their menu to give you a dropkick to the balls of dopamine. FAT! SALT! MSG! HIGH FRUCTOSE CORN SYRUP! REPEAT!
But that requires the stars to align. You need the buns and salad items to not be stale, the chips and meat for the burger to be hot and fresh, the burger to be assembled by someone giving half a fuck, the postmix machine to be set up correctly and give you the right mix, actually fizzy and ice cold. You rarely get the whole meal "just right" but when it is, that one perfect meal sticks in your brain like a catchy song and will carry you through the next half a dozen so-so feeds while you chase the dragon.
These days I only allow myself one trip to KFC a month and I go in and sit down in the restaurant because if something isnt right I go complain and ask for a remake because I spend 29 days a month counting every calorie and tracking every macro because you are not gonna fuck up my blowout meal.
Because when you dont you are now resisting arrest which is so risky you might as well take your chances and just go to school instead.