I've never seen someone write decisions or the intent they started with in commit messages. Even the solutions today that auto-generate commit messages just summarise the diff.
This was helpful when humans were the only ones reading the history. But for agents its useless.
You may not have seen enough good repos. The following is an example commit from freebsd
https://cgit.freebsd.org/src/commit/?id=ac5ff2813027c385f903...
A proper email is like an email. You have the first line as the subject and it may be enough to explain the intent of the diff. But sometimes it’s not enough and you add more details in the body. I strongly believe that people who write the WHAT again don’t know that there’s a diff attached to the commit and think of them a separatete objects. GitHub and VSCode do not really help in that regard.
When you think of the patch as an unit of idea and the commit as the means to convey that idea, it takes the same amount of effort to write an email message.
BTW you do not have to write those for every single commit. You can always rebase interactively and create a final set of commits for sharing. No one cares about what’s in your local copy of the repo.
You could have found this if you did just a little research before declaring an open standard.
The Linux kernel is another great example. Random commit from yesterday:
https://github.com/torvalds/linux/commit/d56b5d163458c45ab8f...
A proper commit message is like an email?
But also, if you look at large projects like Linux or FreeBSD, commits there explain why as well.
When that commit gets implicated by `git bisect` and all you see in the message is exactly what you’d see by reading the patch anyway, you’ll wish the author answered why they did what they did. This, especially, when the author is no longer at the company.