Why is it easier to drum fingers from little one in than from thumb out?

Because your pinky is weak! I think because when you go pinky in then your pinky gets to go first. The pinky is the shortest and it is easier when he is first. If you drum really slow thumb in you can see that the finger next to the finger that is druming pops up a little. Since the pinky is the smallest it takes him time to push down. And the ringfinger can easily get down because it is about one section bigger than your pinky. Also your fingers get longer from your pinky (except for first) so it is easier to drum on the table.