I learned that construction is not really something that I do well. I hire contractors.
I guess, this is the key to understanding different situations. There are people that are good at one thing, and there are others that are good at other things. In ideal situation, to get something done one should assemble right people to do parts of work. Now, the question is, how often do we have "ideal" situations? Personally, I'm still looking for one. In real life, finding someone who will do reasonable planning within reasonable time and reasonable cost also requires to be good "finder". That is why, I guess, in real life people are trying to find workarounds for the "proper" way you have described. The way is indeed proper, but very often not applicable. IMHO.