If you are not in PTP or on deployment, there is not reason a command shouldn't approve leave. That doesn't include training command students--they're there to train.
Sometimes people have an inflated opinion of their own importance and blame it on the job. Othertimes, commands don't manage their people effectively.
As a whole, barring some unusual circumstances, e.g. the aforementioned deployment, a CGI in the S-Shops, an ALMAT or CNAF downstairs, etc, no one should be so important that they can't be missed. We're a military organization--theoretically, anyone should be able to DIE and the others should be able to carry on. If someone can't miss 5 consecutive workdays without the world ending, then their division, department, or squadron needs to unscrew itself and cross train a little. I recently had the CO take leave while the XO was TAD--that shows trust in one's subordinates, and shows good leadership.
I don't disagree with your sentiment as I agree that's the way it should be, but what if there's only 5 or 6 officers in the squadron (at the time), including the CO and/or XO? Losing one FCP to leave hurts, even more so if it's also the MO (or OpsO) and at the end of those 5 days, the CO/XO is going to want to know why another bird isn't up that was supposed to be up or what's the situation with that range event/DLQ/etc that's coming up.