which literally everyone can easily do themselves

Key word here is 'can'. People can update it themselves, but unless kept accountable for missing something bad, they don't do it unless a PM drags it out of them. In a perfect world we'd all show enough accountability to share the info that could affect a project in a democratic and orderly way, but even when ignoring a lack of PM experience, people usually feel it's bureaucratic and takes precious time away from their specialisation.

A PM with a good background will definitely have a chance to be better than a PM without, but being able to contact the right specialists at the right time and keeping the project flowing is what truly matters.