Many of them don't require any kind of authentication, just clicking a button.

Is it just a case of "monkey see monkey do" (decision makers see it everywhere, so they also want it), do lawyers really think that giving people pages full of "you must not use this wifi to break the law" T&Cs is necessary, or does it serve an actual technical purpose like soft-disconnecting devices after N hours to minimize background traffic or keeping noisy IoT devices from blindly connecting to the open WiFi?