I think one issue is that the admissions for medicine are getting harder and harder. In many places you practically need a 4.0.GPA, volunteer work, great mcat scores, research experience, sometimes a post grad degree like an MSc and PhD etc. This selects for highly competitive and intense personalities that are not always suited for every medicine specialty. Most of them don't want to go into family medicine and pediatrics because it's more work, less money, less prestige etc. The friends I had who wanted to go into family medicine couldn't because of the admission requirements. Their only alternative was to have family money to pay for medical school in places like Ireland.

Edit: I should have mentioned that pediatrics and family medicine represent a large proportion of available residency spots each year and are rarely full.