That's a subjective preference. Maybe for some repos it's a good idea to allow or even require longer messages, but certainly not all.
For example, after seeing many different strategies for commit messages over the years, my own preference in many cases is now to permit only one-line commit messages, with a strict character limit, which include a reference to a suitable source such as a feature or bug ID where more details may be found. With git, this can be checked using a pre-commit hook.
The big advantage of this is that a `git log` or similar command with a single-line format can never then hide anything important. Assuming we're talking about an established project that does have things like a bug tracker and some sort of structured project documentation set up, I have found that any time I am tempted to write a longer commit message, there is usually a better place I could record that information, and if not then maybe it wasn't that important anyway.
YMMV, of course. As I said, it's a subjective preference, and no doubt there are many different ways a team might choose to use their tools.
The character limits are a real thing in git culture. One could start here, with a question posed by an apparent skeptic:
https://stackoverflow.com/questions/2290016/git-commit-messa...
git log would definitely show the entire commit message, so I don't see why there would be almost no audience. git blame along with git show or git log -n1 would also allow you to see the rest of the commit message for a particular line in the codebase.
git log could show the entire commit message, but I can't remember the last time I saw any developer whose default format wasn't a single-line one. Presumably there are some people who do prefer to see the whole message every time, and maybe that includes you, but IME that's quite rare.
By default, it shows the entire message, and, in my experience, most people aren't going to change the default behavior in one specific case.
That is true, but I literally can't think of any developer I've worked with in many years who had not done something like that. The typical display in every GUI for git repos that I've come across in recent times is also geared to single-line display, though some of them are marginally better with at least indicating the presence of additional lines than git's own one-line display formats in the CLI.
YMMV, and apparently it does, based on your second paragraph.
Yes, however, -m does encourage people to make single line messages.
More like most times when people look at logs they will only have the first line visible anyway.