I don't think this has anything particular to do with "slopcode", you make a thing and throw it out for the world to see, and the default outcome is nobody even cares enough to shrug. They didn't measure the "other" projects, but I would bet there's also a significant % that get abandoned.
Yeah I feel like you could run a similar analysis on random non-AI Github projects and get the same result. Most of them never go anywhere.