Does anyone still use GitHub?
Yes (https://gitcharts.com/).
There hasn't been a reason to stop using GitHub.
Microsoft embracing and extending the free software ecosystem is not reason enough?
You're about 7 years late on criticism of Microsoft's acquisition of GitHub.
They have not taken any steps toward enshittifying it, and even if it did, it would have to be a very nontrivial change to cause people to stop using GitHub.
I think you mean no new reason.
what do you mean 'still'?