They’ll continue selling these, purely because of two reasons:
On an Air, 8gb is the bare minimum that is realistically viable, for people who don’t do anything than browse the web, who they can later upsell, when they get a new machine.
They can immediately upsell you for every extra memory tier you would need. This makes them a colossal amount of money.
Practically all of us know that the difference between these memory modules is pocket change, when mass produced like this, but for those extra couple cents, they get an extra 100$ from you