But that's the thing: git is very close to a blockchain!

The only thing that's missing from git that makes it not quite a blockchain is that the way we use git doesn't expect there to be a linear series of commits. But with relatively little effort you can add that to git, making a blockchain out of it.

What blockchains do in cryptocurrencies is not magic: they're just the basic auditing mechanism that allows everyone with a full node to verify that all the rules are being followed by parsing all the transactions. The simplest way to do that is with a linear chain of blocks that you validate, starting at block zero.

All the "magic" is in the consensus mechanisms that decide which chain of blocks is in fact the real chain, not the blockchains themselves.