I'm old because Sunday cartoons are no longer a thing for me.
Saturday. The thing is as far as I know -haven't checked in awhile- in the US Saturday cartoons are pretty much over since most of the networks that used to do it cancelled their cartoon programs, and the ones that are left don't generally have enough new programs they show on early mornings on the weekend.
Anyways, streaming has pretty much ended weekly programs like that in the US.
The reasons it still exist in Japan is because of the six day school week, and tradition -the biggest anime were always shown on Sundays and their is no reason to change it-.