And I'm explicitly rejecting the theoretical discussion of "contracts not preventing things", a somewhat useful model of legal thinking for first year law students to understand one aspect, but an absolutely atrocious model for a layperson to understand general contract law.
This is like saying criminal law doesn't prevent crime, which again under some literalist and pointless definition sure a murderer isn't physically prevented from murder by a law, but the punishment of murderers does prevent many people from becoming murderers.
Similarly, contract law influences the behavior of people who agree to them by establishing damages and liabilities for various situations, and these incentives influence and control normal actors in predictable ways. A summary of the influences and controls on normal actors in contract negotiation could be "contracts prevent things".
My contract with my ISP prevents me from reselling my bandwidth to my neighbors. It doesn't physically prevent me, but it establishes a liability for me that I want to avoid.
My contract with my car insurance company prevents me from working for Uber. It doesn't physically prevent me from clicking Sign Up in the Uber app, but it establishes limits on my coverage such that I would be driving illegally if I were to continue, and I want to avoid that, so the contract prevents me from doing it.