Once you understand how git works under the hood it's actually fairly easy to predict that performance will be poor. A simple checkout involves accessing 100s if not 1000s of objects. Also, you can't fetch these all at once because the objects you need to fetch are determined based on a nested tree. So you have to query the tree all the way down, getting each nested tree or blob based on the previous tree's contents. So ultimately you're doing 100s-1000s of queries for any given git command. Each query is fast, but even at 1-2 ms per query it adds up quickly.