No way to know for sure, but I'd guess the number of employed developers writing blogs and having personal projects is in the single digits. For developers with more than 20 years experience, I'd be surprised if it's even 1%. I've got more experience than that, which means I have an extensive network of former colleagues at a similar experience level and I don't know one single person who blogs about tech or works on personal projects. We all have busy family lives and plenty of money so absolutely no need to spend any personal time doing work related stuff.
Not to mention github profile eval would be much easier to game in the age of LLMs if it were to become mainstream. You can already kinda see the effects of these with people sending you mindless PRs fixing grammar and whatnot if you maintain any popular projects.
