What is the difference between concurrency control in operating systems and in trasactional databases?

Recently I'm learning concurrency control techniques in transactional databases. However, I am so confused about the differences between concurrency control in operating systems and in transactional databases. Within my understanding, the concurrency control techniques introduced in database literature can be used in a multithreading program, whose threads share some variables with each other, and vice versa. The techniques used in multithreading programs for sharing variables between threads can also be used in databases for concurrency control. Why do we bother to introduce this differently in database literature and in operating systems?