Problem is, its price goes up, while its quality stays "OK"... At that point you might as well eat somewhere that serves better food for a few more $
But half of relevancy is branding, the other half is delivering. McD has advertising dollars still (also they own other successful franchises such as Chipotle), and in some places in the world it's not crap. It's just another over-priced food chain with some weird marketing attached.
[0] https://finance.yahoo.com/news/mcdonalds-once-owned-90-chipo...