(aka at least in the US they can basically charge whatever they want extra if you demand your old parts)
That's because the old parts are worth money. Check how much extra they want if you request your old tires after getting new ones. Hey, they took money off! Because folks might want your old batteries but they sure as hell don't want your old tires.
It generally is, but in this case the insurance paid for it. I'd think they would be the ones that could do that.