I'm sure the reason for steel cases is simply that they cost less. The price of metals has probably tripled in the last decade. Maybe more than that. Steel cases can be made cheaply.
In the back of their mind they may realize that this will hurt reloading, allowing them to sell more ammo. On the other hand, many of us reloaders don't buy steel cases, so that hurts sales.
Think about Hornady. Their business is reloading. Even they are offering steel cased ammo.
Reloading is a big industry and I think getting bigger. We are much more likely to be threatened by the govt making it illegal than not being able to buy components.
I have a few midway and cabelas catalogs from 7-8 years ago that I flipped through. It is interesting how much some things have gone up in price, and some things haven't.