You can provide a lot more USB outlets than it's feasible to provide regular AC outlets. If they're USB A outlets you know they're only ever going to draw 7.5W

You can provide a lot more USB outlets than it's feasible to provide regular AC outlets. If they're USB A outlets you know they're only ever going to draw 7.5W give or take max so you can slap many more of them on a single circuit than you can AC outlets where people could plug in a bunch of 60+W laptops or USB-C PD chargers.