Can I get a truly variable speed 'dimmer' switch to control a fan?

I have a simple portable fan for summer days. It's 20 inches, and draws 100W at 120V at the max (of three) settings, 75W at the minimum. Even at minimum, it's too much, so I want to install an in-line dimmer switch on the cord. Even though some switches say they can handle 200W, they state quite clearly not to use them on fluorescent ballasts, transformers, or motors.

I get the first two, but why not motors? Variable switches exist for fans (pic related), but they too are three-speed. What is so different that a truly variable dimmer wouldn't be appropriate?

Inductive load is the problem. When first switched on, they’re an open circuit.

>>106164616
Thank you.
So worst case scenario would be using the dimmer switch to slowly bring up power until fan starts moving? One would have to be aware to start somewhere high up, then only bring it down?

>>106164680
Some potentiometers go from the off position to max output with a click. You could get one of those.

>>106165225
Thanks again.