Unless you also consider Dilbert to be a conspiracy theorist...

People are often optimizing for their own goals, instead of the goals of the organization they are working for. People are stupid. People are running on a corrupted hardware. Put these three facts together, and you will see organizations where managers sometimes make genuinely bad decisions, and sometimes they make decisions that help them but harm the company; and they will of course deny doing this, and sometimes they are simply lying, but sometimes they honestly believe it.

Often the quality of a decision is hard to measure, or perhaps just too easy to rationalize either way. When a manager makes a bad decision, it does not mean that the project will fail. Sometimes the employees will work harder or take overtime to fix the problems. Sometimes the company is lucky because their customer is even more dysfunctional than them, so they won't notice how faulty and overpriced is the delivered product. When a manager makes good decisions, it does not mean that the project will succeed. Sometimes other managers that are supposed to cooperate with the department will sabotage the project to get rid of an internal competitor. Sometimes there are unpredictable forces outside, for example a new competing product appears on the market, and it happens to be better and cheaper, or just has better marketing. -- And of course, when a project succeeds, the typical manager will attribute it to their own smart decisions, and when a project fails, there will always be someone or something else to blame. It's like in politics.