Yes, my experience is that Github isn't actually universal. I've yet to work for a company that uses it, personally. My only interaction with Github is in the hobbyist realm when I want code from an OSS project that is hosted there.
Worked at another company circa 2015 with around 80k employees (not sure how many engineers) that used git + cgit + Jenkins + JIRA.
Bitbucket has a lot of Jira-integration and a lot of large corps are in Jira for the long haul now and "might as well get the synergy of Bitbucket".
Plus, don't underestimate the sunk cost fallacy factor keeping a lot of large corporations locked into things like Perforce and ClearCase.
I made a filter list for uBlock Origin (and compatible) ad-blockers that can hide many of the social media aspects of Microsoft GitHub to make it a bit more tolerable when forced to interact with it due to project lock-in.