Why `fiber::mutex` yields in `try_lock` even after acquiring the lock successfully?

Recently I'm reading the source code of `fiber::mutex`, I noticed that`fiber::mutex` will yield in `try_lock` no matter whether holding the lock or not? What's the considerations behind it, and can we just return immediately after lock? Thanks in advance.
https://github.com/boostorg/fiber/blob/238487b543e8863c647d31a82ccfc3fa11a960d9/src/mutex.cpp#L43-L60