> Do people not merge master into their branch before pushing? All that seems like mostly problem caused by having too long living branches.

On projects with a high commit velocity and a large team, simply merging main and running the tests is not enough. The likelihood that a new commit lands on main before your tests finish is high, and restarting the process every time there's a new commit is time consuming. Merge queues are the only way to ensure that main does not break from conflicts that arise "in between" commits.