It used to be very easy on Technics, and I made some for the early Yamahas. The last ones I made were for PA80, but only two.
You can do them as well or better than factory styles, but there is a learning curve and it takes some time.
It used to easier because the parts didn't have so many variations, fills, intros, endings, breaks--all of which should be programmed if you are going to do it right.
Personally I haven't had much trouble finding everything I need in the past few years.
I wouldn't buy a keyboard for which I KNEW I'd have to program a lot of styles. But then someone else may have plenty of time to do that and wouldn't mind.
DonM