The only problem with the 28-ga is that not enough folks shoot it, so the limited demand keeps ammo costs high.
I really believe that the popularity of the .410 and 28 gauge are backwards. Why can .410 shotguns be found in many gun safes and 28's are as common as honest politicians? You have two shells with similar payloads, one throws out viable patterns, the other patterns more like a full-auto rifle.
Some things in the shooting world make little sense.