Massive amounts of doctors won't accept Medicaid, and the list is growing every sigle day. That's because reimbursement rates very often don't cover the cost of care.
Under these circumstances, why in the world would you expect supply to increase? You think thousands of the country's best and brightest young minds will be lining up for 11 or more years of school and residency, living in relative poverty while doing so, working absurd amounts of hours, taking on crushing debt, for the ultimate reward of losing money and laboring under a massive bureaucracy which serves to limit the relationship between doctor and patient?
That's an absurd thing to believe.