There's some fine reasons to use blocking I/O. Often you don't have anything to do until it comes back, so it's the most natural way to write it. For a very short system call, it's faster to make it blocking because you can resume the thread instantly without the overhead of however you send/handle an async reply. It avoids space leaks, because a blocking call will… block if it can't make progress, so you can't send an infinite amount of async calls.

And it means backtraces in gdb work.