Similarly to many other countries, the US has a concept of "adhesion contracts" - essentially, contracts where you have no realistic opportunity to negotiate the terms, and your rights are constrained much more than the rights of the party imposing these terms.

Courts often look at these contracts differently, but around the world, they allow them to exist because they are useful. A good example are the "terms of service" for public or private transit. If the carrier can't define some common-sense rules, like that you can be kicked out or fined for not wearing pants and playing bagpipes on the bus, it'd complicate things.

The legal standard is basically that the rules hold unless they're unreasonable or unconscionable. But of course, what's seen as reasonable depends on the country, the state, and the judge.