Why do college dormitories have to install signal jammers?

Now more and more schools will install wifi jammer in dormitories to prevent college students from staying up at night to surf the Internet and play mobile phones all night.
The principle of the wifi signal jammer shielding WIFI is that the signal jammer will send out the corresponding frequency when it is working to interfere with the mobile phone to receive the normal frequency sent by the router so that the mobile phone cannot connect with the router and cannot surf the Internet normally.