Doctors are incredibly politicised and senior doctors have no qualms throwing junior doctors under the bus (speaking demographically), in exactly the same way a

Doctors are incredibly politicised and senior doctors have no qualms throwing junior doctors under the bus (speaking demographically), in exactly the same way as pilots do. A union doesn't work so well when there's sizable power differential between members, and that's the case with doctors. The political power of a senior consultant with tendrils into management is usually orders of magnitude more than that of a fresh graduate.