Or extremely incompetent PMs. I've had one PM be confronted with the documentation of something where it clearly said "don't do this, it's wrong and will ruin everything" (which, totally by coincidence, is what he was told by someone on the team before). He still demanded it to be done because he had heard a talk at some conference where that was recommended. It took getting the CEO into the issue via back channels to clear that out.

Imho the percentage of PMs, POs etc that have no clue what they are doing is much, much higher than in any technical role. If they're good at bullshitting, they can usually talk their way out of being blamed for their failure and switch to a different company later.