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.
"The person who makes a success of living is the one who sees his goal steadily and aims for it unswervingly." -- Cecil B. DeMille