The usual definition of “linear history” is equivalent to what you see with “git log --first-parent”. Linear history doesn’t mean that people share every “wip” commit from their private feature branch with everyone else.

With linear history you squash everything into a single, working commit which is applied to the tip of the shared branch. The rationale is that each change is like a published piece of writing: it will have been through multiple drafts and final versions as well as being edited and peer reviewed, but ultimately the only thing any of your peers care about is the finished work. None of the incomplete, broken, or unreviewed intermediate versions belong in the shared history and they can be thrown away.

Two counter points to this. First, the code review discussion is often recorded forever but in a social tool that’s kept separate from the code itself.

Second, if you end up being as famous for your code as Austen, Thackeray, Shakespeare or Da Vinci were for their literature then your “work in progress” commits and v0 drafts are very valuable and worth keeping. The amount of people this could apply to is not a large number.