It has to do with their shape and how its 'grain' is oriented in the molding process as well as how they are magnetized. During my brief time at Champion Slot Car Products, we switched from ready made motors and tweaked versions to a new line of uber performance motors using AlNiCo and it was a steep learning curve even with Union Carbide doing the vast majority of the design work to meet our size, performance goals.

I still have some of those magnets and trust me, even though they're too wore out to take a decent charge, they're still way more powerful than a brand new ferrite of a similar size.

GM