How do mobile users receive short messages from telecommunications?

Short message content pushed by the three major operators

Why do users receive such messages?

In fact, the Ministry of Industry and Information Technology had previously requested:

20 18 1 1, the notice issued by the general office of the Ministry of Industry and Information Technology, shows that before the end of March 20 19, all basic telecommunications enterprises and mobile resale enterprises should improve relevant technical means and have the ability to provide domestic mobile phone users with call number labeling reminders and risks by means of short messages and flash messages.