Because of nuclear sharing which would never really happen anyway. But it’s a great way for the americans to say: “you got to buy our shit, we make sure nothing else is compatible”

Without sinking to your level I will limit myself to say:
I am not the idiot here.

Nuclear … takes care of all of its waste

That could not be further from the truth.
There are temporary solutions for the waste at most.

Or maybe somebody knows how to tweak Samsung calendar to accept calendar synch with an open-source protocol?

I use “DAVx” to sync my nextcloud-calendar to/from my samsung-phone.

If your provider uses the caldav-protocol, that might work for you