[shiroiushi]

In the US, rural areas have cultures that prioritize guns, meth, and eschewing advanced education. It should be no surprise that doctors (i.e., people with advanced education) wouldn't want to live among such people, and the only way they can get doctors to work in rural hospitals is to offer huge financial incentives such as medical school loan forgiveness.

[GJim]

So do some urban areas.

[shiroiushi]

They do, and those particular urban areas also tend to be "healthcare deserts" for similar reasons. However, many times the bad urban areas aren't geographically very far from more economically prosperous areas, so it's not that hard to transport patients with more acute needs from the bad parts to hospitals and doctors that can treat them well. This isn't true for rural areas: the distances are just too great.