Employees are never only paid based on value. If that was the case, janitors would make great money, since having a clean work environment is very important and valuable.
What you're missing here is leverage. Janitors don't make much money because most people are capable of basic janitorial tasks, and thus they have little leverage in the job market because they could be easily replaced.
In the case of Gitlab, employees in hotter job markets have more leverage because they could more easily find a high paying job where they live. People living in weaker job markets don't have that. Gitlab is paying the former group more precisely because they have more options.