I totally agree with you. And to add to your point, the impact of having a dominance in the market of "personal project repos" extends far beyond individual developers paying money on their personal accounts and/or becoming paying customers when they start their own companies.
If you think about mid-sized software companies (~10-100 devs), if 80% of your developers have a strong preference for Github over Gitlab or Bitbucket, then that company is likely going to stick with Github or decide to move to Github eventually. I think this is where Github captures much more than that 12% revenue that they are giving up right now.
I am confused by this sentiment. Wouldn't moving to another product (like bitbucket or gitlab) put you in the same boat (since they also offer free private repositories)?
If you think about mid-sized software companies (~10-100 devs), if 80% of your developers have a strong preference for Github over Gitlab or Bitbucket, then that company is likely going to stick with Github or decide to move to Github eventually. I think this is where Github captures much more than that 12% revenue that they are giving up right now.