The idea of miles didn't start because people were clamoring for them. It started because the airlines, first AA and then the others, saw them as a way to lock in frequent travelers. It worked.

If the airlines stop giving us miles, or if the miles cost more than each of us subjectively thinks they're worth, goodbye lock-in. Absent AA (in my case) miles and the benefits that go with earning a bunch of them each year, my incentive to put all my flying on AA goes down a lot. Not to zero, I still like them and their services fit my travel needs, but a lot. I don't think AA wants to take the risk of that happening. (I don't mean with me, they could survive losing me as a customer, but across the board with all the people who are similarly situated.)

I also see situations where companies will not reimburse business travelers for the added cost of miles, since the company gets no benefit from them (and may suffer because of them, since they often motivate travelers to travel in ways that are not optimal in cost and/or schedule from a business point of view). Including "free" miles in more expensive tickets addresses some of this problem but not all of it, since business travelers don't always pay high fares.

The bottom line is that airlines give miles because it's smart marketing. I don't think they'll stop.