A growing number of websites support dark mode theming, but not all of them. When I open a page in reader mode and switch to dark theme, I don't expect logos in the text to fade into the background. Svg is also often much larger than a font file, especially one that's subset.

While it's not svg or on the open web, I have a particular hate for sborn.jpeg in ebooks, as I read my ebooks in dark mode at night and having occasional section break symbols (ornaments) white on black is particularly irritating. Other unnecessary images often found in ebooks include bullets, chapter titles flourishes, letters with accents, and even the chapter title itself.

Not advocating for font icons but one advantage is that their color can be styled form the page CSS - for SVG that only works if the SVG is embedded in the HTML, not if it is loaded externally or from data URLs.