The problem is that the value of #TDD is not obvious, which makes it hard to
make it a default method for software projects. There are always managers,
colleagues and customers that need to be convinced.

Unfortunately it's not a universally accepted hygiene factor, but needs buy in
from all stakeholders.

You cannot secretly do TDD, it affects at least anyone in the software delivery
chain. So even if we know that it works, we still need to put a lot of effort
into making the entry to TDD easy.