I think that one of the biggest reasons you see more plastic out there is because of price. A nice quality revolver will cost quite a bit more than a quality plastic semi auto. For that matter an all metal/alloy framed semi auto will cost more than a plastic framed semi.
I used to not like revolvers, even though my Dad's old H&R .22mag was the first handgun I shot. My wife wouldn't shoot a semi so we got her an inexpensive Rough Rider. I understand the quality is not there compared to a S&W or other nicer revolver, but that gun is really growing on me. That trigger sure feels nice, even with it being an inexpensive gun.
I think if there were more quality revolvers available at the same prices as Glocks & XDs you would be seeing more revolvers. People are not going to drop so much $$$ on their first of anything, especially when they are unfamiliar with it.
Please also understand my above statements are based on prices of new guns. NOT a used revolver vs a new polymer.