log why the permission is denied

It's not about 'the admin of the box' - that is no longer even a concept that makes sense in many use cases such as phones, or even a corporate environment where the IT department might have better things to do than investigate every 'permission denied' error returned to every user. It is about giving the application the details it needs to report a clear error messaage to the user. Otherwise why have error returns at all? Every syscall could just return 0 or 1, and if you want more info the administrator can easily grep the log files....

Returning meaningful error indicators to userspace does not preclude writing to a log file as well. In some cases, yes, security requires giving a terse 'permission denied' error with no further details. That situation is not the norm.