Because if you say "News feed" people are thinking Facebook or Twitter feed. RSS is widely known as it was already integrated in browsers before as a "RSS" button if the site advertised that in the html head.
I should think that’s a pretty niche memory among people who browse the internet nowadays, but then I only have anecdotal evidence, so I could be underestimating it. Even so, I think conflating a general type with a format specification is not a good idea overall.