Don't forget the economy of scale. The cheap brass is normally the most produced brass (9mm, 223, AK rounds, etc). Tool up for it and then make a ton of it. I asked Nosler if they planned to make 220 Swift brass. The answer was that volume demand was not high enough, so "no". That logic helps the small 'niche' producers stay in business, particularly on certain ammo like that for Cowboy Action Shooting. It costs money to make the brass, so if there's fading market demand, they will consider ending production runs. The profit margins are probably pretty thin on some of the calibers that are somewhat generic, like 380. That might be different on some of the low volume, high dollar rifle cartridges like Weatherby uses. Pay 2 bucks a round for 380 and there will be plenty of shiny new brass.
One thing I learned in corporate America is that it's all about making a buck. It ain't for the suntan or the free whiskey, and I had plenty of the free whiskey.