Both the startups I worked at and the mega corps are all on github or moving there from bitbucket. They are in a bit of autpilot mode in terms of useful new features aside from actions but I can't think of any new bitbucket feature since I graduated and started working.
Bitbucket is not a player, as you said there are only people leaving. Gitlab has a better enterprise posture than GitHub and can be deployed more securely. Most developers aren't unhappy with GitHub, but IT and security teams are.
