SVGs in general seem to have had quite a poor adoption rate. Editors for them are fewer, paint can't open or edit them, and support for them is iffy with even google docs not supporting the format for importing an image.
One big problem with SVG is that the specification is so large that everyone implements a subset, so interoperability suffers.
Lots of XML-based standards of a similar age seem to have suffered from this. There was an idea that there'd be a standard for everything, and each XML-based standard would refer to others when it made sense rather than re-inventing the wheel. But too often the result was that in order to implement standard A fully you needed to implement all of B and C and D which your users didn't really care about, so in practice you ended up with an undocumented de-facto usable subset.
(Though for SVG I think the worst problem is that they didn't specify a fixed subset of CSS that should be supported, which isn't an XML-world thing.)
A side issue is that non-trivial SVG authoring is painful to do by hand, so most people use some tool to do it. But the exported SVG will work on the rendering engine of the tool, not necessarily wherever it gets rendered downstream, and it can be difficult to know which features of your tool will result in rendering issues downstream. And sometimes the error is just missing content, others (like filters) often render the image completely black.
It's like using a compiler that supports one version of an architecture and you need to learn what you can/can't do in the source code that will result in illegal instructions anywhere else.
While Sketch is (imo) the best editor I've ever used for SVG it's also the worst about using weird SVG features that are poorly supported outside like, Safari and Chrome (I think they use the former).
This doesn't match my experience but maybe I'm in a bubble: for open source design and fabrication work, svg is basically as standard as pdf, I'll often convert pdfs to svgs to extract vector art and send it to another process, including 3D mesh editors that can extrude from svg files.
The editor I install on every machine and teach other people to use is Inkscape. The learning curve really isn't that bad, I've seen many kids really take off with it.
Inkscape is so overwhelmingly popular for SVG illustrations on Wikimedia that they've seriously considered just using headless Inkscape as the standard SVG rendering backend, instead of rsvg.
Wordpress is a significant part of the internet (hobbyist and small business definitely) and it still blocks SVG by default due to security concerns because SVG images (like fonts) are essentially scripts/programs, not images.
There are various potential vulnerabilities due to this and you can sanitise images or use correct headers to mitigate the issues, but it's easier for many to just say no and sidestep the issue.
> SVGs in general seem to have had quite a poor adoption rate
I don't know. I'm not sure what the real numbers are but in my experience SVGs are pretty commonly used for app and web icons because they are easily "themeable" (color changes etc.)
A lot of designers I know just keep a raw layered image and swap out themeing on a per-case basis. SVGs are easier to dynamically theme, but usually any theme variants get run by a designer anyways that will tweak color tones for the specific usage as needed.
Just to be clear though - I love SVGs and want them to get more momentum solely on the basis that they're just a way better way to store abstract line art and can yield proper image scaling... I just think a lot of the technical advantages we tend to think of aren't really that valued by designers and get lost in needing to be done manually anyways.
There are plenty of people who do know how to create good SVGs, but my first thought when I read the title was: maybe the people who know how, also know it's better not to.
