The reason people (myself included) rather like good Git commit messages is evident when one compares them to the alternative.

You're working in a commercial/closed source environment and want to find out why line 57 in src/blah/db/utils.py does that. Where do you look?

- inline code comments. Usually non-existent. Often out-of-date, sometimes misleading, frequently tells you no more than you can discern from just reading the code itself (especially now type annotations are trendy again). Rarely explains why the code exists. There's a reason people caution against too many comments, and that translates into people probably not putting enough commentsin.

- calling code? Helpful, but thanks to microservices and increased levels of abstraction (APIs, DI frameworks, messaging buses, config parsing) you've got to go check 900 different repos out to work out what is going on.

- email? Give up. You'll find invitations to the company Christmas party and Q2 sales figures but actual tech explanations are in short supply.

- Slack etc - same problems as email, plus developers who hide away all the interesting stuff in private team channels

- Google Docs - you probably don't have access to the relevant doc, and there's no way to know that you don't

- wiki/docs? Half baked, wrong etc. Or it'll be autogenerated JavaDoc type stuff that'll tell you what you already know or can reasonably infer from the code. Also, findability sucks. Or the developers just avoid the whole thing because the software is nasty and corporate and barely usuable.

- bug tracker/ticketing system? You ask around and someone says "oh yeah, Dave made that change two years ago" and then you search for tickets that match related keywords only to find out that those tickets weren't brought over from Trello into JIRA, and now you need to go ask IT to give you access to the legacy Trello board which they don't want to do because then it'll put them over the five users per month limit or whatever.

- Architecture Decision Records / decision logs / whatever you want to to call them - nice if they exist, I guess.

- ask the person who wrote it? This assumes they still work there and can remember. Plus you gotta do the asking around routine which takes days and destroys all hope and joy in the world.

By a process of elimination, commit messages are the closest you're going to get. They're right there - on your computer, neatly integrated into your editor, hopefully. You can search them fast in a terminal window rather than in some slow web-based monstrosity. If you're lucky, they're actually useful. Even if they aren't, they're at least contextually useful in helping you narrow down your search strategy for the inevitable plunge through email/slack/JIRA/Trello/internal wiki etc.

Ideally what should happen is the really useful commit messages get copied into stable technical documentation like decision logs or a properly maintaned wiki. If people did that, great, but it's pretty rare. A culture of sharing weird interesting tech things in a Slack-type system can help because future devs can at least search but you do that at the cost of more interruptions for colleagues now.

The broader issue is of all the bad options you can choose, it often tracks the wrong thing. In something like Trello/JIRA/whatever, if you're looking for the technical reasons, it'll have the business reasons without the technical stuff, or vice versa. You generally want both, and most systems only give you half the story.