The question is who’s writing the code. A core part of a senior engineer’s job is helping to train and mentor junior engineers; it’s not unusual for an entire project to be designed and led by a senior engineer and implemented by more junior engineers. Design reviews don’t result in commits, deep dives on technical implementations don’t result in commits, negotiating an architecture change between groups don’t result in commits. A large amount of the actual heavy-lifting value-add of an actually senior engineer is not in the code they’re writing.