Why do most AC motors run at 1725 RPM?

Factual Questions
1

I would have thought the standard would be some multiple of 60Hz; why 1725 instead?

2

See http://www.aosmithmotors.com/html/motorDoctor/Determiningspeed.htm

3

You’re right. The theoretical speed is 1800 rpm. However, due to friction and other factors, the actual speed ends up being anywhere from 1775 to 1725 RPM.

4

I have nothing to add to the OP, but I wanted to jump in and thank mks57 for that excellent link.