This rule doesn't stop them from kicking anyone operating a wifi hotspot out of their hotel, or stop them from requiring anyone who enters the hotel to submit to being searched for wifi equipment. The only thing it stops them from doing is jamming the public airwaves. They are allowed to prevent people from operating wifi hotspots in their hotels, but they aren't allowed to use illegal means to do so.

Analogously, movie theaters are allowed to stop people from bringing in outside food, but they aren't allowed to assault someone to take away food that they brought in.