Even if they just replicate what these companies are doing I think there's two main benefits:

  1. less waste. The entire case is being thrown away immediately by these volume consumers. All the packaging and what not is also wasted.
  2. easier/cheaper deployment. Companies are already paying their employees to design replacement cases, control boards, etc. and getting them built at relatively small scales. Then they're paying them to shuck and transplant from the Mac Minis. Apple could probably charge a >50% premium for their solution vs the equivalent number of Mac Minis and companies would jump on it.

Additionally, at least in my experience, the headaches and fixed costs of deploying these machines means companies refresh them far less often than other hardware. It's totally possible that companies would refresh more frequently if Apple just sold something easier to deploy.