Read the book by Graeber. It’s pretty easy to find a pdf copy online.

There’s a lot of different reasons and it varies depending on the type of bullshit job, the industry, the country, etc.

Here’s a good example. It might make sense to re-train or fire members of a low performing team. But instead you hire more people to basically just redo the poorly done work. It would make economic sense, initially to fire them and replace them with less people and less rework, but morale, pensions or other factors may make firing them unpalatable.

Risk aversion. If you have a team of twenty people who only put in half days of work, well now you can easily absorb double workload when the business needs to.

Maybe a VP has a big ego and demands to hire a big new team. Most people think it’s a waste, but no one wants to tel the VP “no”. Afraid the industry veteran will quit or work. So they get their team of questionable value and it makes everyone feel good that this powerful person now leads more people/teams.

The short answer is the market is never fully efficient. I mean, it can’t be. Not even serious capitalists would expect it to be.

Seriously, read the book. It’s not super long.