Because commit history is here to explain WHAT and not WHY. "Why" is explained by a decision log such as ADR which can be store in the same repo and can be mutated in the same commit that has WHAT in its commit body.
But also, if you look at large projects like Linux or FreeBSD, commits there explain why as well.
But also, if you look at large projects like Linux or FreeBSD, commits there explain why as well.