The NSK bearings in this motor are not bad bearings but,and it’s a big but, the axial load ratings for this bearing are about 160 kg for 1 million revolutions. That’s how they rate them. Obviously 1 million revolutions is not much in an electric motor.
General rule is to divide the rating by 12 for longevity.
So our 6901 bearing is good for about 13 kg of axial load each.
But we still don’t have any radial loads so our bearings are toast!
I’m with you, definitely going to use a thrust bearing.