This particular coven operates as a powerful and wide spanning enterprise focused on accumulating power to direct the world in ways that align with their interests. This group operates similar to HYDRA or COBRA, recruiting members mostly from young people seeking power in society, with the intention of using them to expand the coven's interests. These individuals may rise in the hierarchy due to their successes and eventually become key members and important players. Witches gain more power through a dark ritual, which steals the life force from an unwilling victim and adds it to their own, making their magic stronger. Rituals are performed with a circle of 5, with each witch sharing in the power gained. This means that a young witch will join the coven in the hopes that, one day, she will be promoted high enough to start performing such rituals to eventually become a goddess.
The process of being versed in enough occult knowledge to perform spells takes decades (the equivalent of obtaining multiple PhD's, for example). So a simple human would have to study REALLY hard (while also being a servant for the older witches), for a lifetime, in order to eventually get to the point where the other witches will grant her the opportunity to start taking part in the ritual.
The problem is that many of the higher ranking witches view these prospective members as mooks, using them in irresponsible ways. Higher ups do this to shield themselves from having to do dangerous tasks, leaving lackeys to take all the risks. Using them as expendable shields against authorities or competing criminal organizations, or as run of the mill goons who can be easily sacrificed when they outlive their usefulness, is problematic for long term survival of the coven.
Interns can't exactly unionize because...well, it is a criminal organization. Expecting them to take up pickets and march through the streets demanding equal pay and treatment is unlikely. How can I encourage my underlings to use their recruits more responsibly and prevent them from being expendable?