Investor/ homeowner rehab cost difference?

[Vonetta Booker]

Why does there seem to be such a big difference between what rehabs cost investors & what they cost homeowners? (For example, many investors talk of doing rehab on a 50k budget--but then on the same project, many GCs will charge that much for the kitchen alone.)

Is it because the former buy materials themselves & have subcontractors install them? Do most contractors mark things up significantly? Are homeowners getting stiffed because they don't know any better?