Ok, how does that work out? the manufacturers are businesses, they aren't going to make things they can't sell therefore if they are producing them in great numbers they are still selling so their popularity isn't in danger yet.
It works the same way cars work. The manufacturers make more than one model. While they may not make enough on the revolvers - which in this day and age are very much a niche market, like black powder muzzle loaders - they do make a small profit on them. Or they sell them at a small loss (again, just like car companies) to satisfy the niche market. If you buy a S&W revolver and like it, when you decide to buy a 1911, you might be more inclined towards another S&W product.
The vast majority of the market is semi-autos. But that doesn't mean it's not worth the companies effort to continue to sell products in the niche markets.
You don't think GM makes enough off the Corvette to stay in business, do you?
In fact, as the revolver becomes more and more of a niche item, it may well become more profitable, because people buying them will be buying them as collectibles, and will be more likely to dole out some cash for pretties (polish, coatings, engraving...) that someone buying a gun to shoot isn't likely to choose.