[kev009]

There a lot of discussion here https://retrocomputing.stackexchange.com/questions/7412/why-... but nothing seems conclusive.. I would wager the last answer, "IBM was using 400Hz", to be most directly causal reason. The motor-generator configuration might provide galvanic isolation and some immunity to spikes and transients as well?

[Animats]

Smaller transformers and capacitors in all the linear power supplies. 400Hz is still common in aircraft. Distribution losses are higher, but you're going across the room, not across the country.