In Miami, it is insane for a few reasons:
1) Entitlement in Miami is real. Every waiter is a burgeoning crypto bro and every waitress is an Instagram and Onlyfans star in the making. So, they deserve 20% just for sharing the same air as you. The quality of service has become irrelevant.
2) Many foreigners do not tip, so many restaurants, especially around downtown and Miami Beach, automatically add gratuity.
3) Miami has a lot of lipstick on a pig type restaurants where the packaging is really nice but what is served is still shit. In many of these shit shops, they also automatically add gratuity.
I don't know if you flew through Miami International, but if you did, there are self service kiosks where you pick up a bag of chips or a soda from a fridge yourself, and there is an old Cuban lady standing next to the register where you scan the item yourself, and then the payment system has the nerve to ask if you want to leave a 20% tip for the pleasure of her having looked at you while you picked and scanned your own shit.