The 870 is a great pump shotgun but the express model most people purchase has been going downhill since the 2000s.
I prefer the much stronger and only slightly heavier steel receiver of the 870 over the Mossberg.
They made the express such a budget gun that it required someone with some handyman skills to disassemble and polish them up without overly wearing or damaging anything and make them decent, which is something less and less of the population is capable of or devotes the time to do anymore. Having to deburr and smooth up things.
I understand why they felt the need to do it though, as the AR took over the market they had to keep the price of the shotgun lower than the ever decreasing cost of an AR-15 for the penny pinching segment of the market the express was targeted at, because an AR was preferred by many. A semi auto modular rifle that works from point blank to long range with less recoil, or a chunky shotgun good for just close range meant the only way it kept any market was being cheaper than AR-15s which I think it next to impossible now without making a total piece of junk shotgun.
The other big seller, the remington 700 once had limited competition in its price range, and its high profile use in law enforcement and military allowed them to charge a little more for it. Well it has a lot more competition now, is less useful than many semi auto platforms or bigger cartridge bolt guns in military use, and even some semi auto platforms can be similarly accurate for not a huge increase in price.
Those were probably its two biggest money makers and they just don't command as much of the market. The AR has become THE gun in recent times because it is so versatile and decent entry models so cheap. Modular semi auto that can be heavy or light, long range or short range, scoped or red dot sighted easier and without gunsmithing, etc
That is probably one of the downsides of the AR, it has become such a go to gun for so many people that it is replacing a lot of other guns, and so where restricted a lot of the guns it replaced are not around anymore and don't enjoy as big of a market to keep costs low.
If I had to guess a lot of manufactures have in recent years finally jumped on the AR-15 bandwagon since it was doing so well. Even many that once had competing firearms like Rugers mini-14 jumped in and started making quality AR-15s. If this latest political unrest has them questioning if those guns are now going to make them much money, then they have shifted their business towards a product they don't feel as confident in, and have chosen to cut losses.