I think possibly because it's seen as a model social democracy, which is something the people pushing this line are keen to discredit? I also think the focus on Sweden brings in the ideal of a blond-haired blue-eyed Nordic racial identity; whether conscious or not, I don't think it's coincidental.
Why do they keep bringing Sweden into it?
I guess most Swedish news doesn't tend to be big news so maybe it's easy to make fake news about it and spread it to English speaking countries?