Why does the borrower pay back the money knowing that usury is illegal?

Private lending is a civil legal act and legal.

High interest rate recognized by law. A loan refers to an interest rate that exceeds 4 times the benchmark interest rate of a bank in the same period, that is, when a legal dispute occurs, it supports an interest rate level that is lower than 4 times the benchmark interest rate of a bank in the same period, that is, high interest. Loans are not protected by law.

Because the benchmark interest rate is different in different periods, the legal recognition of high-interest loans is also related to the period. The benchmark interest rate for the same period refers to the benchmark interest rate announced by the central bank. For example, for one year, the benchmark interest rate is 6%, and four times is 24%, which means that more than 24% is legally recognized as a high-interest loan. As far as a year is concerned, 10000, the annual interest rate does not exceed 24% * 10000 = 2400, which is not high and is beneficial to loans.