> Devs were proficient in CVS, SVN, HG, BZR, GIT as a standard
That's completely made up on your end. I've been doing FOSS for 17 years and the vast majority of people were barely competent with any of them at all beyond whatever their chosen ponyshow was (including off-brand ones like Darcs and Monotone), and any switching from a persons preferred one to the use of another project was often met with grunting and complaining, if it was done at all.
The reality is we only think this because we saw people do this, at great cost of their own time -- but that's the literal definition of survivalship bias. For every 1 person doing this 50 just stuck with whatever they used and wouldn't bother. I've literally seen people refuse to contribute to a project over tabs vs spaces, and people still do this with git vs hg today, just not as much today.
More people use Git and contribute to FOSS in a single day in 2022 than every developer who knew all these tools combined back in 2008 or whatever. Whether this is good or bad is up to you, but you don't need to make up claims about developers being epic journeymen in the past and mastering 50 version control tools to do a single days work. They did not.
> Things really became one-sided after github started gamifying open-source contributions, and when a new generation who perhaps grew-up in a more competitive academic setting took it as an opportunity to make their resume more impressive.
Sorry, but I consider this to be a similarly made up claim that's just sour grapes. I've been using GitHub since 2008, I'm one of the first users. GitHub didn't even have "gamified" social features until the past 3-4 years IME (what, stars are about it?), and before that its product was pretty poor in some key areas like code review and project management, org permissions, on-prem control, etc. I didn't even use GitHub commercially until like, 2018, because most orgs had setups that were better in some key areas. But it was pretty easy to use and get started with, which mattered, and still matters, and soon enough nobody could compete with the same ease of use for free projects.
If I had to "blame" "someone" in this vein, a better place to start: global monetary and fiscal policy for the past 20 years resulting in software development becoming one of the only places with rising wages to meet cost of living demands in places like the US -- resulting in an influx of new blood to increase their wages and quality of life, combined with political choices like low interest rates, and huge explosions in demand for software devs for things like VC adventures, etc. Subsequent developments like bootcamps designed to churn devs out to match rising demand, etc which solidified platforms like GitHub further as it was easier for them to paper over these fundamentals when there was a clear winner (git/github) to focus on and ignore everything else. Forest vs trees and all.