You can guess I suppose, but it's simply a guess. I manage my work flow quite nicely by using my calls list (self employed emergency call out engineer) so when I've actioned a call (spoken to customer, closed the call, done the job etc.) and it no longer needs to be in my caller list, I delete that call along with others I've actioned. Deleting the complete caller list would mean I lose all the calls in one go, and either I need to transfer the call list to (as you suggest) another system or spend time deleting them one after another.
Just because one person uses a phone in a different way to another, doesn't mean either is right (or wrong). If you're happy deleting all your calls list in one go then fine, but that doesn't help someone like me who has a different need.
Perhaps I'll just go back to Samsung and let my daughter have the Pixel.