They are not specialized in all domains
As I said before, your contractor is here to help you complete your renovating project and provide you with skilled workers. So, if you hire a contractor who thinks he’s the best in all your areas of interest, well, you are probably making a mistake.
Of course, it’s cheaper to hire a man instead of a whole team, right? But if you want a functional house and to avoid possible long-term repair costs, then you have to understand that you can’t ask your contractor to be an interior designer and plumber and so on.