> What I find strange about this is that in 2020 nobody would be this openly cynical and selfish about, say, good Python idioms, a useful emacs configuration, git shortcuts, etc.

I definitely saw people have concerns about vimrc files and their personal library of shell scripts well before 2020, and I've seen people early in their career get burned by sharing it too. They had a tool that made them productive, it got out of their hands, and suddenly they're getting negative feedback from someone who tried using it and it didn't meet their expectations, or it got checked into the repository and now the script they used at their last job too has their current job's copyright notice and license on it, and they're perceived as being petty for trying to claw back their own intellectual property because they didn't go to the trouble of slapping legalese all over their personal tools.