Having a templating system in ‘that environment’ is worth its weight in gold IMO. I’ve been switching between Svelte and Django templates a lot lately, and Svelte just…knowing about the DOM, makes the experience so much nicer. I haven’t come across a non-JS template system that does this. And yes, I was there for PHP and jQuery and whatever.
A combination of the devil you know and Stockholm Syndrome.
It was better in many ways than the dominant techniques in 2013, sure, but that's not a terribly high bar, especially when observing the React model a decade later.
React served well enough for quick starts. It proved… challenging… for ongoing maintenance and quality control in long-lived projects.
Because it's nicer than most other templating systems, and when you want to add interactivity, it's nice to have everything in one language and paradigm. Plus, static typing support.