They didn't say they're only using the git hosting, they're just not using the issue trackers because that would require adding non-devs. For all you know they could be using GitLab for CI, merge requests, package management, and deployments, none of which require adding new people to the team.

Exactly this, we use it for all of those things. None of which provide value to PMs, designers, and other non-engineer roles within teams that still need to collaborate on issue tracking and documentation.