GitLab is not just a git hosting and collaboration tool. They want it to be the single tool you use for almost everything to do with an application including monitoring, controlling infrastructure, error logging, project management/planning, security auditing, and a bunch of other things.
If you are using GitLab in a hobbyist or solo way, you are touching about 5% of the features that GitLab provides. Which is fine and a valid way to use it but its easy to see how customers justify spending big dollars on the top plan with hundreds of user licenses when the tool does so much. We even have customer support and project managers using the tool because it caters to them well.
If you want you can even use gitlab to replace something like zendesk as it provides an email address which puts all emails in to a "support desk" queue.
