I no longer worry about verb tense, simply using whatever sounds best to me when writing that particular commit message. My messages don't match each other, but so what? They're readable and to the point. Why waste time worrying about something that just doesn't matter?
By yourself it doesn't matter but when you work with teams it is nice to have a consistent style. It's like asking why we have style linters, brand guideline books, and so forth. They're not strictly necessary but it makes things more pleasant to work with. And it takes zero effort to use the imperative.
