The point of Rotom as far as i can tell is that it inspirits devices that have a 'special motor' in them. This is mentioned in many of its pokedex entries, even so far as to say that it can only use a specific model of discontinued washing machine (this also raises questions about the origin of this motor).
But this doesn't explain its ability to inhabit devices like the pokedex since its very clear they wont have a motor like the other appliances.
I wonder if this element of Rotom's design is being lost, because looking up rotom fan-made forms show lots of cool and creative ideas, but most to none have actual motors in them.
If I were to suggest Rotom forms, I would go with;
Blender - Steel type
Garbage disposal - Poison type
Jackhammer - Ground type
Discoball - Fairy
Printer- Normal
Running Machine/ motorised combat aide? - Fighting
Not sure with Bug, Dragon, Dark, Rock and Psychic.
Good point, i forgot about that. Still, it doesn't explain why it's pokedex entry in Violet says the washing machine is so rare that it's traded at high prices. I guess there's not a lot of demand for rotom wash or something