Have you tried this?

git log --oneline 

It's an alias for git log --pretty=oneline --abbrev-commit, and displays the "short sha" and "short description", for example:

9bee8857 Write more code
831fdd6e Write some code Second line of message

The problem is that you are missing an empty line after the first line of your commit message. The command above usually works for me, but I just tested on a commit without empty second line. I got the same result as you: the whole message on one line.

Empty second line is a standard in git commit messages. The behaviour you see was probably implemented on purpose.

The first line of a commit message is meant to be a short description. If you cannot make it in a single line you can use several, but git considers everything before the first empty line to be the "short description". oneline prints the whole short description, so all your 3 rows.

No, that doesn't mean it shows all the latest commits. It shows all commits in the history of branches, tags and other refs, but it does not show commits that are not reachable from any ref. A typical example of a commit that is not reachable from any ref is when you've just run git commit --amend: the previous commit still exists locally, but it's no longer reachable and won't be shown in git log --all. But git reflog will confirm that it does indeed still exist.

As for why --all isn't the default: you normally won't want that. For instance, if you're on branch master, and you run git log, you typically aren't interested in the history of any feature branches, you typically want to see the history of master.

If you do normally want the --all behaviour, I recommend creating an alias.