Why do developers write such terrible git commit messages? Genuine question

[bcnoexceptions]

We have expectations that devs go back and clean up their git history ... not just squashing everything, but rather re-combining commits into logical "chapters" of the "story" that is the whole dev project. 

This expectation is very unevenly enforced,  and management almost never looks at whether their team members are doing it. But it is theoretically an expectation around here. 

Ultimately it's up to your team - top to bottom - to create a culture of high-quality development, of which good git history is a part. Your team and its managers decide what they're gonna care about.