Big unstructured commits are one consequence of not having a trusted system.
Today, I had to make an important change to a project and found out in the process a few minor bugs. I was tempted to fix them on the fly, but remembered one aspect of what makes a good commit: atomicity.
So I just put the changes to make in my trusted system to think of doing them afterwards and realized that one reason why so many people commit big changes at once is very likely because they don’t have a trusted system that helps them forgetting. Therefore, to keep a sense of control, they need to make the change before their brain forget.