I wonder whether the UI of many git clients contributes to this. Even if very long messages are allowed, from what I've seen typically the dimensions of the fields are fairly small. This could subtly give the impression that you are being too verbose and not using the tool correctly.

Even for git itself it's funny that the article you linked encourages people to learn to love git CLI, but recommends a third party tool for writing multi line commit messages for ergonomics.

Clearly it's not a massive technical challenge, as the good examples show, but the tooling seems to inadvertently encourage shorter messages.