Many years ago I tried very hard to go all-in on XML. I loved the idea of serving XML files that contain the data and an XSLT file that defined the HTML templates that would be applied to that XML structure. I still love that idea. But the actual lived experience of developing that way was a nightmare and I gave up.

"Developers keep making this bad choice over and over" is a statement worthy of deeper examination. Why? There's usually a valid reason for it. In this instance JSON + JS framework of the month is simply much easier to work with.

Most of the issues of using client-side XSLT is that browsers haven't updated their implementations since v1 nor their tooling to improve debugging. Both of these issues are resolved improving the implementations and tooling, as pointed out by several commenters on the GH issue.

"Choice" is a big word here. It would imply "we've weighted the alternatives, the pros and cons, we've tested and measured different strategies and implementations and we came out with this conclusion: [...]." You know, like science and engineering.

While oftentimes what happens is is "oh, this thing seems to be working. And it looks easy. Great! Moving on.."

XSLT is much nicer to use if you just create a very simple templating language that compiles to XSLT. Subset of XLST already has a structure of typical templating language. It can even be done with regexps. Then simplicity becomes a feature. You can write your page in pretty much pure HTML, or even pure HTML if you use comments or custom tags for block markers. Each template is simple and straightforward to write and read.