Seriously though, if I were forced to maintain every tiny legacy feature in a 20 year old app... I'd also become a "former" dev :)
Even in its heyday, XSLT seemed like an afterthought. Probably there are a handful of legacy corporate users hanging on to it for dear life. But if infinitely more popular techs (like Flash or FTP or non HTTPS sites) can be deprecated without much fuss... I don't think XSLT has much of a leg to stand on...
Flash was not part of the web platform. It was a plugin, a plugin that was, over time, abandoned by its maker.
FTP was not part of the web platform. It was a separate protocol that some browsers just happened to include a handler for. If you have an FTP client, you can still open FTP links just fine.
Non-HTTPS sites are being discouraged, but still work fine, and can reasonably be expected to continue to work indefinitely, though they are likely to be discouraged a bit harder over time.
XSLT is part of the web platform. And removing it breaks various things.
I couldn't be more happy about its demise.
We built stuff with it that amazed users, because they were so used to the "full page reload" for every change.
Like more or less everyone that hosts podcasts. But the current trend is for podcast feeds to go away, and be subsumed into Spotify and YouTube.
And those that would replace you might care more for the web rather than the next performance review.