Yeah, shotgun technology is in a rut.
Christopher Spencer invented the first successful pump action in 1882, and JMB invented the first semiautomatic shotgun in 1898.
Part of the resistance to box magazine fed shotguns is that tube magazines are better for sporting shotguns, and "good enough" for fighting shotguns.
For sporting shotguns, they are snag free, allow for easier handling and carrying, easily plugged, more easily allow for multiple shotshell lengths, are better for shooting sports, work better for rimmed cartridges, and allow one to carry the shotgun by the receiver. They've also been the status quo for almost 130 years.
It's also more difficult to design a box magazine for rimmed cartridges, and for a shotshell in particular. Rimlock is a problem, multiple cartridge lengths are a problem, and shells deforming in the magazine are a problem.
Most fighting shotguns are just variations on sporting shotguns, and it turns out that since shotguns aren't terribly popular for combat, tube mag fed shotguns are "good enough". After all, why isn't the AA-12 more popular?