How did you come to the conclusion Git isn't scalable in the number of users? There is no limit in the number of users with Git. There may be limits in the number of interaction between those users, i.e. pull/merge requests, clones, fetches etc. But they are mostly limited by humans.
A central system, even a cloud-native system, has far more contention points in operations that are not even interactions between users, i.e. status, commit, etc.