I figure it’s a psychological response to the high tax: if you’re going to shell out $200 just in tax on something, you won’t feel comfortable unless the price tag is at least 4x the tax.
I don’t blame the few manufacturer’s for the unreasonable costs at all. With their Federally mandated fees, Federally mandated record keeping, limited but expensive tooling, labor costs and minimum manufacturing, these costs are justifiable. If restrictions were removed, modern, high capacity manufacturing processes and minimal “hands-on” processes would be developed by many manufacturers and the costs would drop dramatically just as they have for all other firearm accessories - rails, ‘scopes, lights, lasers, magazines, etc.