Has always seemed like a rhetorical device to me. In effect no job is actually bullshit since if it was it would be eliminated. The truest "bullshit" job is one where you are absolutely irreplacable for a single, trivial piece of knowledge. I.E. I'm the only one who can print the records at the end of the year, and otherwise I do (practically) nothing. That's how I've always thought of it, but others may disagree.
Often times it feels like a way for creatives and engineers who make the product to express some (rightful) resentment towards the folks who manage people and business.
There's also jobs that exist as the result of Moloch traps, e.g. many corporations need to keep a lot of lawyers on staff because their competitors are litigious. If they all agreed to be less litigious, they could all realise a huge net savings. I imagine much of advertising is similar, albeit in a less straightforward way.
Often times it feels like a way for creatives and engineers who make the product to express some (rightful) resentment towards the folks who manage people and business.