I think the grandparent poster is referring to something subtly different. It's not that people making the bold pronouncements are incompetent, it's that they may be competent but are not quite as competent as other folks who stay silent, and they're okay with that. Oftentimes an "expert" knows more than the person they are explaining things to - it's just that they may know less than someone else who doesn't bother to explain things.

Somewhat relatedly - there's another phenomena where people may be quite aware of the limits of their knowledge, but deliberately choose to hide it to achieve some objective (usually personal gain, but it could also be in service of some organization or mission), because they know that their audience is more likely to believe confident people. You pretty much have to do this to found a startup, because all startups are inherently risky and uncertain and yet few people will follow you if you seem uncertain.

I think risk is extremely pertinent to this situation.

The (relative) silent expert to those more audibly expressing/pronouncing is also considering the outcomes of releasing information that is highly likely to be correct, and what may come of that information becoming public.

They also take into account the scenario where they may be wrong or only partly correct, and if so what are the long term problems that may result in being wrong (or even in being right - take the heliocentric model of the universe for example). Therefore they may deem the risk too high.

We're still finding out what a search engine monetised via advertising does to the world.