There is an astronomical difference between the effort required to buy tens of thousands of dollars worth of imagery, and the effort required to buy tens of thousands of dollars worth of someone's time. The former is a matter of a cart and credit card, the latter requires lengthy emails, contracts, legal approvals, timesheets, and all other sorts of mumbo jumbo and for most projects, is enough work that I often just don't bother.
Though those roadblocks are there to protect both parties, I suspect that there's an artificially large delta between cost and risk.