I would make a distinction: not forced in the sense of "kicking and screaming," but forced with a huge smile on their faces. In the long run, nobody is forcing the airlines to issue FF miles via credit cards. It started as a way to get additional income from their current customers: people already flying the carrier and who wanted an opportunity to earn more miles. Over time, especially in this age of bloggers, influencers, and churners, it's taken on a life of its own. Look at the stats from the recent Amex-Delta announcement:

Consider that the pre-tax profit at Delta for 2018 was $5.1 billion. There is some cost to DL for miles redeemed (whether it be fuel/catering for seats redeemed on DL that otherwise would have flown empty, or compensation paid to other carriers for partner redemptions), but I would guess that quite a bit of the income received from Amex ends up as profit. Sure, DL may have been forced to greatly increase the cost of awards, especially those without capacity restrictions and especially those on premium-cabin international routes, as those are most likely to displace revenue passengers (both in terms of the seat taken, and in terms of someone redeeming for travel that they otherwise would have paid for). But they do so not kicking and screaming, but with a smile on their face, due to the amount of money they're getting from Amex from the co-branded credit cards.

The fact that some of us around these parts are moving away from the co-branded airline credit cards and to other opportunities (such as independent-currency cards like CSR, or simply cash back cards) once we figure out that the returns given by the airline cards are no longer the best deal after the ongoing devaluations and lack of saver award availability are taken into account, is an interesting fact but largely irrelevant, as long as revenue from the co-branded cards continues to increase at a rapid pace. This must be because the rising customer base from the general public that reads outdated advice from a blogger (that happens to get a spiff from all new signups from the links they publish), or sees an aspirational video of int'l premium-cabin travel on YouTube and wants to get some of that for themselves, is outpacing defection from the core group that originally got on the co-branded card bandwagon. As long as that phenomenon continues, expect all current trends to continue as well.

Like all bubbles or fads, it will eventually come to an end. At some point, enough people will realize that there are better deals out there than putting their spend on airline credit cards. Once that happens, the whole thing will collapse: banks can't survive just on the churners, as they are always money-losing customers. Churners aren't really an airline problem directly, at least not currently. But once enough people abandon ongoing spend on airline cards, leaving churners a high-enough percentage of miles awarded, the whole thing will collapse. And it will be impossible for either banks or airlines to fix it by just taking a step or two back. I think we're still several years away from this happening, and it shall be interesting to watch.