While I do worry about github, I disagree that the dominance of git is a problem. At some point every industry grows up and standardizes on something, anything, because any standard is better than no standard.
Git is far from an ideal solution, but it has emerged as the standard way to manage version control in a software project, and we benefit from there being a standard. Version control is the first barrier to entry in starting on a new project, so having an industry standard for version control benefits everyone: open source projects get more contributors, companies don't have to train new hires on their system, and employees have one fewer barrier blocking them from specific jobs.
Could we have standardized on a better system? Certainly. But launching a competing standard at this point isn't going to make things better, the best case scenario is that it fragments the industry.
Git is far from an ideal solution, but it has emerged as the standard way to manage version control in a software project, and we benefit from there being a standard. Version control is the first barrier to entry in starting on a new project, so having an industry standard for version control benefits everyone: open source projects get more contributors, companies don't have to train new hires on their system, and employees have one fewer barrier blocking them from specific jobs.
Could we have standardized on a better system? Certainly. But launching a competing standard at this point isn't going to make things better, the best case scenario is that it fragments the industry.