To be honest, as a private school teacher who finally landed in a public school, I am very aware of this problem.
As a private school, the mobility of personnel is very large. Let me talk about my own personal experience. 18 years, worked as a teacher in a private school in a county with strong first and third lines in a southwest province. This school is a well-known local school, but it still can't keep people. Teacher recruitment is very frequent, and the summer and winter vacations are the peak of recruitment. Why? It is because the holiday is the peak of teachers' collective resignation.
First of all, as a private school, interests are always the focus of the school's consideration, so it is decided that it needs to constantly squeeze the labor of young teachers. Overworked working hours, teaching tasks, and various assessments are really unfriendly to teachers, so we took a summer vacation. Teachers quit in batches, and more people quit during the winter vacation. Naturally, private schools need to recruit people during the winter vacation.