The problem as I see it is that you are classifying someone who doesn't want to come to work during a period of annual leave that has been approved and already started, as someone who "just expects to take".
That just isn't the case at all. In this situation the employer is looking to take, and needs to realise that when asking, and be prepared to give in return.
No, you're still misunderstanding me.
Leave is leave, and I do not expect anyone to come in. Or be obliged to give a reason.
But, I will notice who is prepared to put themselves out to help. That person, if you like, scores points. I'm more inclined to help them. Give and take. Like, recently, one of my best staff wanted to pick relatives up from the airport early one afternoon. I could, quite reasonably, have required a half-day off to do it. Instead, I said just go.
Had I asked them for help half a dozen times and got a blanket "no", why should I?
On the other hand, had they said "sorry, can't because..... " then fair enough. They're certainly not obliged to come in on days off, or provide reasons. They're employed at x pay for y hours/days, and the contract says z days off.
Saying "no" doesn't count against them. At all. Ever.
The give and take is that it cuts both ways. Nobody is under obligation to come in on a day off just because I ask. They're entirely welcome to just work expected days, and hours. But .... I'm not required to give time off on top of that, or promote them, or give extra overtime in preference to others, either. Those that won't help out if asked can't expect me to bend over backwards, either.
But saying yes counts for them. They help me, I'm more inclined to help them. However, I don't see it as a negative if someone I'd expect to normally help can't, for a specific reason.
This is not some sort of formal system with points in a ledger or anything. You just get to know people's attitudes. Some just want to work contracted hours for contracted pay. Fair enough. Some have a more positive attitude, will stay longer, come in early, do things they might not normally do, help supervise a starter and so on. But even people I'd normally expect to be willing to come in sometimes just can't. Something is going on, and even if they want to, they can't. That's what I mean by good reason, that however much they might normally help out, sometimes there are good reasons why they just can't.
If someone wants to abide by strict contract provision, that's fair enough. There's no negative impact from me. I'm getting what I'm paying for. But don't be too surprised if I take the same attitude back. And don't expect to jump the promotion queue either.
I have come across those that think that because I cut Fred some slack, I'm obliged to cut them the same slack, never considering that Fred helps me out when I ask and they don't. Most managers and employers notice who has a constructive, helpful attitude, who is just doing a day's work for a day's pay, and who is a malcontent with a chip on their shoulder. The first is promotion material, the second is fair enough, and the third can often be a liability. I'm not suggesting anything about where the OP falls, and those categories are a gross simplification. But we all read people and attitudes, and are more inclined to put ourselves out for those that will, or have done likewise.