Although they weren’t called styles back then, it all started in the late 60s/early 70s when manufactures started adding auto accompaniment features to their organs, eventually the arranger keyboard developed which gave you all the easy play features of the organ in a light and cheap keyboard package.

Styles are in essence just Midi Loops so can be included on any electronic keyboard instrument, however because of the limited capabilities of arrangers (Just one keyboard with minimal real time controls) styles have become paramount to get a decent sounding performance out of them. (Manufactures have always designed arrangers for the Home Hobby Market rather than pro musicians, as it allows them to sound great with minimal effort)

Hope this helps

Bill