That's good. It's good that everyone is on board with removing such a pointless feature that comes with a significant maintenance burden and security risks.
What? XSLT in the browser is an awesome idea. It let web sites publish data unencumbered by presentation and let the client's user agent decide how to use the data. Your browser can download the XML and use a linked XSL stylesheet to display it for a graphical browser. That exact same data resource could be used instead by a program that understands the schema of the data and do some custom thing with it.
There's no need to trust some giant blob of JavaScript to convert a data document into a usable web page. Just the native XSLT engine (using the same XML processing pipeline it uses for all the other XML it encounters).
A web of XML documents could all be easily viewable by a web browser but the exact same data can be processed with other tools. There's a lot of old web API ideas being recycled (poorly) with JSON to service AI tools today. The web could have already been nicely structured data easily ingested by autonomous tools (AI or not) while at the same time being still perfectly accessible by graphical web browsers.
But no, everyone decided that because Enterprise XML Usage was icky so they needed to completely throw out XML in favor of a much shittier serialization format.
The reason it is a bad idea is because XML, XSLT and related standards are almost impossible to implement. I don't think there is any non-broken implementation of it. The idea behind it is interesting but the actual standards and libraries involved are awful.