I think conformity effects play a huge role in this area. The large majority of modern philosophers all have similar educational and cultural backgrounds. They go to elite universities. They read the standard Western philosophical canon. They work very hard to publish a lot of papers in prestigious journals. They are friends with other academics and with other high achievers in the "standard" fields like finance, law, and medicine. Their parents were probably academics or from the upper middle class. They have spent most of their lives in a university setting.