There's pretty much always several plausible reasons for why a change was made. What's interesting is knowing exactly which one, especially when it later turns out to be wrong!

What a change does is self documenting. Why it was made and why that specific approach was chosen could be due to many things, such as:

* business objectives,

* the result of experimentation,

* the result of an offline conversation

etc.

This cannot be captured in code alone. This is why we write commit messages.