Why do many companies require an internship in Beijing for half a month or a month when recruiting deliverymen?

Now such advertisements are everywhere. Don't be fooled. When you die, you will lose a layer of skin, drain you, or buy your kidney. Just think about it. When you arrive in Beijing, you will be asked to go to a place with only one mobile phone number. Who will you call if you have a question? I don't know where the police are. They don't have a stall in the local area, but their salaries are generally higher (4,000-8,000) and their jobs are easier. They can't recruit people in Beijing, so they have to come all this way to find you to recruit people?