Like many management system fads, it started as a useful kernel of wisdom or obvious maxim that idiots ran with and turned into a monster. In the case of six sigma, the idea is about constantly optimizing your workflows and not accepting "we've always done it this way" as an excuse.

But most people lack the critical thinking skills to correctly apply wisdom when necessary and instead need a solid framework to operate within. That's how these things inevitably develop. Just like how Agile is supposed to be about getting working code over being bogged down in process but inevitably ends up with with half baked products that have massive issues.

Six Sigma also gets applied to industries it has no business being in. The mentality works best when you have a fixed workflow. In manufacturing it would be if you are making a lot of one thing. You can do a lot of optimizing. But I have seen it employed in organizations where every project was vastly different. Instead of a lean approach it should have, and previously was, following a house of quality philosophy. This happened to be in an industry where cost was rarely a consideration but performance and reliability were.