When Cairo exports to SVG, it converts all text to outline shapes. As you’ve seen, the drawback is that you can no longer edit the text; one benefit, though, is that the document no longer has to refer to some specific font file installed on your computer, and so can be freely moved/copied/placed into other documents without you having to worry about moving/copying the fonts as well. This is also good for fonts where the license prohibits you from copying/sharing them.
When Cairo exports to PDF and EPS, it doesn’t convert the text - the resulting file includes the shapes of every character you’ve used in the document. So you can freely move and share the document, again without worrying about missing fonts. And the quality might be better, since the outlines are generated as needed, when the document is finally rendered.
You may also be able to open the PDF file in an editor (Affinity Designer/Adobe Illustrator, for example, and possibly also some PDF editors) and you “may” even be allowed to edit the text in the converted document - particularly if the specified font is still available, in case some characters weren’t included in the original. Then you export to, say, SVG, at which point both AD/AI allow you to control whether to include the fonts in the SVG or not (an option which unfortunately Cairo doesn’t offer).