That's a completely useless observation. Past US gov't policies have placed an absolute ceiling on the number of new physicians that can be licensed in the US annually, resulting in a shortage that probably will continue for the rest of my lifetime. The US now has fewer physicians per capita than most of the other large, economically developed countries. There is a shortage of physicians, so pretty much any competent physician can work as much as he or she wants to work. If the number is down, it's because fewer want to work part time, not because there isn't enough work for them.
That's true but the article did not say differently.
Somehow I suspect that a “part time physician” will be assessed the same huge insurance premium as a full-timer ... therefore his insurance cost per patient is greater, and this would greatly discourage such behavior. I don’t know a single part-time physician, for what it is worth.