Why do some asteroids tumble end over end?

Well, what's the difference between rotating and tumbling anyway ?

I look at it this way:

-- When you walk around and spin a basketball on your finger, it's rotating.

-- When you roll the basketball on the floor, it's tumbling end-over-end.

What's the difference ?

According to the basketball, there's no difference at all.

The difference to US is:  Which way is the spin-axis pointing ?

-- If the spin-axis is pointing up-and-down while the ball moves around,
then we say it's rotating.  Like the Earth, the Moon, and Mars.

-- If the spin-axis is pointing side-to-side while the ball moves around,
then we say it's tumbling end-over-end.  Like Uranus and some asteroids.

To me, all the planets and asteroids are just rotating.  But WE have
different descriptions for it when we compare the rotation to the way
they're moving around.

That's my opinion.  I could be wrong.