There’s a silly cliché / quotes that says

“You don’t know what you have t’ill it’s gone”.

Probably a repo guy

And as cliché as it is. I think it’s true.
It’s probably linked to hedonic adaptation, where things that used to make us happy don’t after a while. Winning the lottery wears off, getting a raise wears off, that new “thing” you bought that made you so happy, wears off. etc etc.

I suspect that might be why things like retreats or lent are so effective to get people to be grateful. If you go without something or someone for a while, you appreciate it more… At least until you re-adapt again 😉