Coaches are more likely to tell women how to play I suspect. Men would pushback a lot and not want to change, and women would be more receptive to critique. Obviously Im stereotyping, but thats just what I think.
As for why they want everyone, not just women, to learn spinny serves, its because spin serves are the best type of serve. They can be ramped up indefinitely, and it teaches you variety. Also, you do not ever want to double fault, and spin serves is how youre gonna avoid it without doing weak serves.