[BigJono]

Because software projects fail for people reasons, and people reasons are usually subjective.

If you have a tight team of experienced devs building a simple CRUD app you can do almost anything short of building the thing in Polish BASIC with triple spaced lines, and you'll still get a result. Likewise if you have a team with 8 managers and your best dev has only done a couple of courses on codecademy, no set of engineering approaches is going to save you.

And that's just the factors within the engineering team. For every inexperienced team that doesn't deliver a result, there's 10 teams that are gutted from internal politics or management decisions, and 100 startups that fail to find a market fit. On the flip side of that, every month or so I find either a showstopping bug or a new puzzler of a UX decision in one of Uber's products, but it literally has no bearing on their success as a company. The simple fact is it doesn't matter whether they do TDD, or scrum, or whatever, as long as they don't do anything truly catastrophic.

Basically, the majority of success factors for the majority of projects come from outside the engineering team. And the ones that don't will be dominated by the team's basic development skills, which makes the signal much worse for measuring the effectiveness of anything from a project management, high level architecture, or testing perspective.