What do you think their real reason for wanting to remove XSLT is, if not what they claim?
Reflexively siding with the tech majors is about as dogmatic as reflexively siding against them.
https://news.ycombinator.com/item?id=44778764#44778850 - "Meta AI gave people a "share" option with several levels of click though required to share a post and it was a fiasco"
https://news.ycombinator.com/item?id=44752546#44755224 - "Claude Opus 4 is 5x the price of Claude Sonnet 4. I don't think it's 5x as good."
That is not a combination of words that should be mentioned in the same sentence as the word XML or, even worse, XSLT.
XML has its value in enterprise and reliable application development because the tooling is very old, very mature and very reliable. But it's not something taught in university any more, it's certainly not taught in "coding bootcamps", simply because it's orders of magnitude more complex than JSON to wrap your head around.
Of course, JSON has jsonschema, but in practice most real-world usages of JSON just don't give a flying fuck.
XSLT has been around for decades so why are you speaking in hypotheticals, as if it’s an up-and-coming technology that hasn’t been given a fair chance yet? If it hasn’t achieved that by now, it never will.
XSLT is designed to work on XML while HTML documents are almost always SGML-based. The semantics don't work the same and applying XML engines on HTML often breaks things in weird and unexpected ways. basic HTML parsing rules like "a <head> tag doesn't need to be closed and can simply be auto-closed by a <body>" will seriously confuse XML engines. To effectively use XSLT to extract information from the web, you'd first need to turn HTML into XML.
It doesn't need to be some big conspiracy: they see the web as an application runtime instead of being about documents and information, don't give a fuck about XML technologies, don't use them internally and don't feel anyone else needs to.