Initially, LinkedIn was just another site where you could find jobs. It was simple to use, simple to connect with others; it even had some friendly groups with meaningful discussions.
And then it gained monopoly as the "sole" professional network where you could actually land a job. If you are not on LinkedIn now, you are quite invisible in the job market. Recruiters are concentrated there, even if they have to pay extremely high prices for premium accounts. The site is horrible now: a social network in disguise, toxic and boring influencers, and a lot of noise and bloated interface to explore.
When Google decided to close their code.google.com, GitHub filled a void. It was a simple site powered by git (not by svn or CVS), and most of the major open-source projects migrated there. The interface was simple, and everything was perfect. And then something changed.
GitHub UI started to bloat, all kinds of "features" nobody asked for were implemented, and then the site became a SaaS. Now Microsoft hosts the bulk of open-source projects the world has to offer. GitHub has become a monopoly. If you don't keep your code there, chances are people won't notice your side projects. This bothers me.
Rant over. I hate internet monopolies.
GitHub is not likely to follow that trend just because it has more value for them if it sticks around. They bought github, I think, for the branding as they've struggled immensely to get people to trust team foundation server and later azure devops brands because they sucked so bad early on. Using GitHub to put an entry-point for azure focused products in front of a huge audience is sly as well. Microsoft only needs to extinguish things if it is a threat (usually when they don't own them). They're happy to buy successful brands and roll them into integrations with their other products, making partnerships with growing orgs hard for said org to avoid. That's what they want possibly more than anything as big enterprises take ages to begin working with entirely net new partners so they look at who they already have agreements with.
I don't think anyone needs to be on github that's just there for OSS projects (ie. being hosted on gitlab or somewhere else should be fine so long as it is public and search-indexed). Internet search and content aggregating platforms are good enough at getting me to where I need to go. GitHub's search has never really been useful for me on that front.