Almost no cars, trucks, or tractors are steam based anymore. I believe most ships are ICE as well, not to mention rockets, and animal/muscle power. As such I’d need a very deep analysis of the situation to believe any claim. (deep because in an ICE a large part of the power comes from burning fuel producing steam, so we can start debating how much of an ICE is steam - have fun).
In any case my local electric utility generated more power from wind than all customers used last year, so I can make a good claim most of my power isn’t from steam. If your utility isn’t in the same situations or close you should be demanding they get with the times.
If you don’t have a sensor then that is cheaper in the short term, but it quickly wastes a lot of energy running when the humidity is under control. For a dehumidifier you need more energy to get lower so the room well generally will be fairly consistent not too low humidity even as outside humidity changes, but you will use a lot more energy than a system that turns off when humidity is good.
there are purely mechanical systems that used to be used. However they have some weird machining requirements so it isn’t clear they are cheaper than a digital system (this partially depends on volume - make more and the machining gets cheaper per unit). The digital system is as we already have established is very cheap and lets you put buttons and LEDs on the unit for a few cents more - this is far more valuable to marketing than the possible savings (if any!) from a mechanical control.