> I'll never understand why we can't all agree to just make the price the price.

Not sure if you're being rhetorical or not, but the reason is very simple: Sellers want it this way because it makes their job (selling you stuff) easier. The sellers are the ones in charge of the laws about selling (there are a few scattered consumer lobbying organizations but they are nothing compared to industry lobbyists in basically every industry). As a result, the preferences of consumers do not matter, at least on the margin.

Mostly rhetorical. I do believe that if a super-majority of consumers revolted, sellers would be forced to make changes. Tipping is a good example of where social norms are playing a big role along with the law.