Why do university teachers call candidates to enroll students during the period of volunteering?

In order to attract students, some private colleges and universities, especially partial schools, have special enrollment groups, some led by teachers and some led by students, to publicize the school. I will also buy student materials (probably sold by your class teacher in senior three). Call for publicity and enrollment. Every recruit has hundreds or even more commissions! Of course, there are also very good schools that will call students who have achieved particularly good results in the college entrance examination.