Earlier quoted context omitted.
RSS likely isn't the only thing that uses it. XSLT is basically the client side declarative template language for XML/HTML that people always complain doesn't exist (e.g. letting you create your own tags or do includes with no server or build steps).
I understand that there are more possible uses for the tool, but RSS is the only one I saw someone mention. Are there more examples? It may be that I don't notice when I use it, if the page just translates itself into XHTML and I would never know until opening the developer tools (which I do often, fwiw: so many web forms are broken that I have a habit of opening F12, so I always still have my form entries in the net…
I think I've read some governments still use it, which would make sense since they usually don't have a super high budget for tons of developers, so they have to stick to the easy way to do things.