There is no federal vacation requirement. The fed doesn’t even require breaks. It defines what is/isn’t considered vacation, sick time, breaks, etc… But it doesn’t actually impose any requirements for those things. It simply defines what employers must do if they choose to provide those things. And lots of states essentially just went “We don’t want to make any labor laws of our own because that would be communism, so just follow whatever the fed says.” So lots of states have basically zero requirements for things like breaks or vacation/sick/personal time.

Lots of national companies will impose company policies to follow whatever the strictest state requirement is. Simply so they don’t have to deal with training managers differently in those more protected states; They can simply create one training manual for the entire company. So employees in those unprotected states still usually get things like breaks or vacation simply due to company policy. But that doesn’t mean they’re legally entitled to those things, it simply means the company doesn’t want to get Department of Labor complaints in the more protected states.