It's called the "golden rule", they who have the gold make the rules.

OK, seriously, they don't technically get to decide what makes a binding agreement, a judge does that. But US law and US judges are very business-friendly. I mean there's the whole invented crime of "identity theft", whereby a bank who is defrauded by an individual gets to pass off their victimhood to a completely uninvolved third party.

I'm a US attorney but not in contracts. Contracts is a fairly complicated area of law, and the fundamental common law of Ks that you study in law school tends to be very different from how Ks work "on the ground." Most notably, statutes currently exist that change the way this common law operates in sometimes non-obvious ways. Standard disclaimer here that this is in no way to be construed as legal advice, this is not my area of expertise; take this as high-level background.

Essentially, under the common law here, all that a contract needs in order to be valid is three things: a valid offer, a valid acceptance, and valid "consideration," where consideration is a legal term of art referring to 'something of value' gained through the agreement.

The idea is that, there is no servitude. Companies can offer whatever terms they want (subject to a very few number of restrictions, dependent on the industry/regulatory domain). You are under no pressure to accept. You can easily reject the terms by simply not using the product. Courts have generally been reluctant to prevent parties from agreeing to whatever lawful thing they want to agree to. The main exception is that you cannot have contracts which serve 'an illegal end.'

In the US, there's no need for a contract to be written or overheard at all. There need be no written document, no witnesses, no record whatsoever. So long as there is a valid offer (obvious jokes are not held to be valid offers, for instance), valid acceptance (you generally need to affirmatively signal acceptance, but this need not be oral or even explicit), and valid consideration (really nothing more than a formality nowadays, this is why many deeds say "exchanged for consideration of $1"), the contract is valid, even if it only exists in the minds of the two parties.

Obviously, proving such a contract can be difficult, but it can be done, particularly if the parties were acting in accordance with the terms of the claimed contract. If we orally agree that you will start working on building a shed for me, you buy supplies and deliver them to the site, but then stop work, you can't claim the contract never existed, because you've acted in accordance with that oral contract.

In this area specifically, there's been some progress made in getting the courts to understand the enormous power differential at play here. You nearly can't survive in this country without at least one credit card, and if all the major companies' cards have terms like this, then you don't really actually have a choice in the matter. It's been a slow process however.