Considering that Winchester model 97 riot guns were used by American troops in the Philippines during Spanish American War that ended in 1902, and were already in the Winchester catalogue and not a special order item your statement is not factually correct. In fact every successful repeating shotgun from the 1900’s onward was offered in a riot gun configuration from the factory.
Up until the late 90’s shotguns were by far the most popular long arm for both police and citizens. They only recently fell out of popularity because:
A. the North Hollywood Bank Robbery/ Shootout ( https://en.m.wikipedia.org/wiki/Nort...ywood_shootout ) shootout where they (shotguns) weren’t effective due the distances involved the bad guys using body armour and police only having buckshot. This led to the wide-scale adoption of carbines by police departments and the dropping of shotguns by same. At the time police/swat were the biggest influences on popular gun culture and gun mags were full of “death of the police/combat shotgun” articles for the next decade.
B. Expiration of the AWB which meant that new gun buyers could now buy new AR mags that didn’t cost $60-$100 dollars each and reliable brands other than Colt became available on the market.
C. The Global War caused the drivers in the market to go from Police to Military and those guys were killing the shit out of people with carbines and by the mid 2000’s had really worked the kinks out of the design, and refined manipulation and technique to a level that we hadn’t seen before. Plus, optics and accessories were improved and proven in field use at the same time.