Dispensaries won’t allow you to work at other dispensaries?

What is up with dispensaries not allowing their employees to work at other dispensaries? It just seems a bit unfair to offer part-time, minimum wage positions with a huge societal stigma attached, and then not allow employees to work at another shop to supplement income. Especially in a state like California where non-compete agreements don’t exist. I served/bartended for years before moving over to cannabis and it would be absolutely laughable if management tried to prevent their employees from getting a second job. What the fuck?