> A description of what changed is very useful when browsing through git logs.

Doing a blame on a file, or just looking at the diff of the pull request gives you that. The why is lost very fast. After a few months it is possible that the people that did the change is not anymore in the company, so nobody to ask why something was done.

"Oh, they changed the algorithm to generate random numbers". I can see that in the code. "Why was it changed?". I have not clue if there is no extra information somewhere else like a change log, pull request description, or in the commit comments.

But all this depends on the company and size of the project. In your situation may be different.