Developer is also a professional with experience/refinement so he knows the magic specs to make things, magic things to say in the emails to the bureaucrats, magic words to put on the applications to avoid getting fucked by a bunch of "you need a survey for this" and "you need an engineer for that" and "akshually since you've done this you need a new septic" type landmines that cost $1-20k individually the little guy is gonna run right into.