[kaitai]

Frequent = a test every ten years in internal medicine and some continuing education/maintenance of certification. Even that is under attack (http://knowledgeplus.nejm.org/abim-moc-petition-reveals-deba...).

Doctors are human and some are constantly learning new information while others aren't. There are a lot of pressures on them that are perhaps orthogonal to "learning new things" and "keeping up with the best evidence."