Great question! I considered that, it's what lead me to the idea to use DNS in the first place. The problem I had with that is that the ultimate URL path might change, not just the hostname. What happens if a repo has to move from github.com/org/repo to mycoolforge.net/repo?

But there's also another reason that I realized as I was working out the details of git-remote-helpers: What happens if your remote needs to change protocols? With doink you can swap from http(s) to ftp with an ip address instead of a hostname, or perhaps even some (future) git-over-whatever-p2p-network.

So yeah if you're swapping from a github-style forge to another github-style forge and you don't need the flexibility, you definitely could just CNAME it! And that would probably be more robust, but it would also give you less future flexibility :P