 Why is Git a DAG?

Because a Git commit can have more than 1 parent due to merge commits when you do:

It can even have more than 2, there's no limit. Although that is not so common (with good reason, 2 is already one too many): softwareengineering.stackexchange.com/questions/314215/can-a-git-commit-have-more-than-2-parents/377903#377903