Version control systems gave us a lot of quality of life features but left us with an enormous problem - hosting.
Hosting was bothersome. You had to set up a server and make sure the server stayed up otherwise folks couldn't get to your code! You had to deal with access control and other administrivia. So much tiresome toil.
This is a problem that corporations were quick to offer solutions for. They came to us with an appealing offer: give us your code and we'll host it for free. After all, being the primary host for the world's software is an advantageous position. They could offer premium services for power users and businesses and leverage the goodwill of the open source community to score those deals. These companies are not hosting our software out of goodwill, they are hosting it so that they may take advantage of and extract capital from our work.
So throughout the history of open source we have a pattern of putting all of our eggs in one or two baskets. But eventually a company needs to make money - so they start boiling the eggs in the basket. SourceForge infamously started distributing adware and malware. Google Code shuttered its doors but was kind enough to provide a read-only archive. BitBucket removed Mercurial support. And so on and so forth.
When the eggs get hot we quickly move them to the next basket. Rinse, repeat.
So GitHub comes along, gains critical mass, and nearly all of us put our eggs in that basket - StackOverflow's 2020 survey showed that 82% of respondents use GitHub.
If open source is a garden then we keep planting ourselves in sand and hoping the tide never comes in.