A physician shortage may be a bit much, but it appears that physicians overestimate their availability based on a study by Coffman et al. (2016).
The percentage of callers posing as Medicaid patients who could schedule new patient appointments was 18 percentage points lower than the percentage of physicians who self-reported on the survey that they accept new Medicaid patients. Callers were also less likely to obtain appointments when they posed as patients with private insurance.
This fact that physicians overestimate their availability should not be a surprise. The cost of inaccurately estimating ones availability are asymmetric: physicians who overestimate their availability will only upset potential patients who won’t become there patient and could even build an air of exclusivity. On the other hand, understimating the availability means that a physician may become idle. What is surprising, however, is that this bias occurs for both Medicaid and private insurance; because Medicaid patients are less lucrative, one would expect the overestimation of availability to be much higher for Medicaid patients.