It's all pretty simple. The airlines are free to charge for anything they want. We, as the consumers, are free to move along to a different airline.
But...it's going to be like
Walmart soon. They come into a town, they slash their prices for a year or two, then when they have forced all the other shops in town out of business, their prices start creeping up.
Once we start losing those 'cheapo' airlines, we are going to see fare increases.
If you don't like a fee, don't use that airline. Anyone who thinks their bags are really free on SW is fooling themselves. You just aren't seeing the charge. It's pretty much the same as DME. Sure, you aren't paying oop for it, but it's getting paid for somehow. And that somehow is reflected in room rates. Even if you don't use DME, you're paying for it. Same with SW and those free bags. Those flying with carryon only are still paying baggage fees...it's in your fare already. But, we Americans, feel better if we can't 'see' the charge.