Why would I agree to be bound by any legal system other than the one that favors me?

Most states have by statute or judicial interpretation held that when a one-sided contract (ie. insurance contract) is entered into that any ambiguity is to be resolved to the favor of the party that did not draft the contract. If I am an insurance company I don't like that rule so I add a clause that says you agree to be bound by XYZ Law which provides that if there is any ambiguity in an insurance contract it is presumed that there is no coverage.

The vast majority of contracts that people enter into are not "bargained for exchanges" but rather you accept the terms as written or see if you can find another provider with terms you like better.