What surprises me more than the missing guages is that some manufacturer of firearms and ammo hasn't figured out he is missing marketing opportunity by not producing shotguns to shoot several more gauges than we currently have. They seem to have no problem reinventing rifle cartridges eg .308 Win, .30-06, .300 Win Mag, .300 WSM, .300 Ultramag, .300Weatherby. There has never been a year, I don't think, when some new "super" cartridge hasn't appeared to fill in an imaginary gap in the rifle or pistol ammo spectrum. But we have been stuck on standard 12ga, 16ga, 20ga, 28ga .410 for half a century if you overlook the 3 1/2' 12ga which is a very poor substitute for an 8ga or 10ga. I think a 32ga would be lovely for dove and quail. Of course I also know I can load a 20ga to duplicate whatever standard loading the 32ga would handle just as I currently load it for 28ga duplication at times. American style skeet with slow targets and premounted gun would probably benefit by restricting the guns to nothing but the 2 1/2" .410. There is no significant scoring difference in the other guns to differentiate who is best shooter of the day anyway.
