Engineering is a profession not a craft. You draft up the plans and instruct people on how to build it, you don't really build it yourself.
The appropriate craft skill is stonemasonry.
Really the biggest problem is that knowledge engineering and profession engineer both exist and overlap a bit.
However Profession Engineer is Wisdom based, which is highly unrealistic. (as an engineer with multiple degrees I can attest to this directly).
You are wise enough to be able to know the difference.
But for the sake of game balance, Crafts are INT based, while Professions are WIS based.Why? Because the profession roll is not only the knowledge, degree and know-how about that profession, but also knowing how exactly you can earn money with it.
Not all engineers are employed, and know you know why.
Or rather get paid much less then the qualit of their work might warrant.
When we learned about major engineering failures, it was always a wisdom problem, not an intelligence problem. Wisdom-based profession likely represents the care and attention to details to re-check load distribution when a supplier changes brace types. Realistically, it should take both, but that's one way of making sense of it as things stand.
You're obviously just a terrible businessman. There are far too many examples of brilliant inventors who died bankrupt.