You might not stay on or join a WL - and that’s great too.
But why would they remain? Because the want to - and that’s reason enough.
The person OP is describing has chosen to remain - if it’s true they have no intention of changing and OP doesn’t know what’s truly on the mind of the person described…I mean, what if they WL school offered a financial bonanza?
Nonetheless, what ever they are thinking - they have that right - and if they are offered, they will simply not accept or let the time period to accept lapse.
That’s their right - whether anyone agrees with it or not.