Many places today such as restaurants, malls, and other public places have free and open WiFi that does not need a password or login information to access. That means that anyone, even people outside the building that contains the router, can easily access the network. Since there are no accounts or similar, even with logs it is almost impossible to identify a specific user (especially if they spoof their MAC address).
So, how do those places deal with abuse or illegal activity? That includes uploading/downloading illegal files, criminal activity (threatening emails, leaking information, etc.), or hacking (denial of service, capturing network data from other users).
Basically, is it even possible to deal with abuse and identify a user who has committed a crime or similar on a public network when thousands of people use it every day?