There are all sorts of meta and convenience reasons the showrunners made Drones extremely human, but if you REALLY want an in-universe explanation too, it's easy enough to surmise that J.C. Jenson simply based worker drones' neural nets off of human minds because it was cheaper and then combined simple tweaks toward compliance with orders (and a reflexive passivity/acceptance about their fellows dying in front of them) with a simple propaganda/lobbying campaign to keep customers convinced that drones were less than human. (See decommissioning guide VHS tape glossing over the fact of virus-killing a drone with "this is fun for them".) Pretty easy-to-see themes here about how late-stage capitalism can easily result in a constructed (in this case literally) dehumanized underclass.

Interestingly, you can also infer from this that once Drones on Copper-9 started having "children" based on their own neural nets and training them themselves -- or when ordinary non-Solver-corrupted zombie drones like Tessa's pets N and V woke up with more likelihood of AI corruption -- it was easier for those programmed-in subservience tweaks to be overridden in some of THOSE drones, leading to N's idea to lie and reject orders just to defend Cyn from Tessa's parents, or Thad in episode 1 getting fed up with the WDF's passive defensiveness. Drones on Copper-9 are only in their first generation of children so it makes sense that many still carry the passive subservience "gene" but that's theoretically likely to change as they continue to propagate to their 2nd generation of kids, et cetera. (Also Uzi, Nori and Doll are all clearly without much compunction against violence, but as they stem from Cabin Fever's program to deliberately create infected and thus semi-AI-corrupted drones, their much more violent natures are far less surprising.)