Relative permeability is the characteristic of electrical steels that lets them carry magnetic fields. M19 steel has a permeablity ~8500x higher than vacuum[1]

Relative permeability is the characteristic of electrical steels that lets them carry magnetic fields. M19 steel has a permeablity ~8500x higher than vacuum[1]. Permittivity is the characteristic that allows dielectrics to transmit electrical fields. The vast majority of dielectrics are <100x higher than vacuum permittivity, and they're very unsuitable to make a motor out of. Materials with high permittivity have fairly low breakdown voltages. Also, humans have very low breakdown voltages; high voltage motors are often dangerous to be around. Fundamentally it's because materials lend themselves much better to magnetics. [1]: https://pdfs.semanticscholar.org/9303/19ba00b3c7329308df24798c4ec177d2946f.pdf https://pdfs.semanticscholar.org/9303/19ba00b3c7329308df2479...