Progressive enhancement work well for simple stuff. Like progressively enhancing a form post, or a "like" button which just sends an Ajax request. But as the complexity grows, progressive enhancement doesn't really scale and you end up with two separate versions of your site/app.
I agree that Javascript only apps are often less usable, because the devs making them aren't testing enough on different browsers and devices. But the trend of the "Javascript only" approach is certainly driven by more than just frontend devs that want to use shiny new things (even if that is a factor as well).