Another point to consider is that one person can do all of the jobs required to get the parts made.
Not all people, when a person is made to wear many hats, (take on many different responsibility's) things suffer usually quality and efficiency.
Some people can over come this, more people can't or are not willing.
"You say I started out with practically nothing, but that isn't correct. We all start with all there is. It's how we use it that makes things possible." -- Henry Ford