I'm certainly not advocating for a return to C + ncurses, but there's a wide ocean of options between that and HTML+CSS+JS in the terminal.

Yes, for simple projects, absolutely. But when you're shipping something as widely adopted as CC, I disagree. At the end of the day, you're making a UI. It happens to be rendered via the terminal. You still need accessibility, consistent layouts, easy integration with your backend services, inputs, forms, and so on. If you don't need that stuff, there are lots of other, simpler options. But if you do, your other options begin to resemble a half baked, bug filled reimplementation of the web. So just use the web.