Companies will give out coupons for products that don't sell so well.In my experience working retail, this just isn't the case, in general - unless it has changed in the last decade. Coupons have a couple of purposes: Loyalty and foot traffic, much like sales, and often on things they make a decent profit on. You wind up seeing Tide laundry soap, Gillette razor blades, and so on. CVS gives coupons on CVS brand items to promote their store brand... which keeps folks coming back to buy stuff they make a decent profit on.
Coupons are very likely to happen on new products, too, as a way to entice folks to buy them.
It also costs money to put out coupons, either physical or digital, in no small part because you have many retailers that need reimbursed and coupon fraud is definitely an issue as well.
Simply put: Coupons are an advertising device.
Often, products that aren't selling well are either taken back by the manufacturer (to be sold at places that sell discontinued stuff) or marked down by the retailer with absolutely no fanfare (like a coupon). Folks that coupon a lot (or extrememly) are often getting new or established products at a good price instead of things they won't find in 3 months.