There are some quad copter controllers that try to deal with single motor failures, but they're mostly experimental (at least on the hobby end to the space) since they need to be able to reverse a motor, which most motor controllers used in these applications are not build to do.
Found a vid: https://m.youtube.com/watch?v=bsHryqnvyYA
Losing them, crashing them, having people steal them or throw them in a lake - those are things to include in your VC funded "operating costs" and to mitigate/offload the risks in your TOS...
(Small print: "The delivery customer shall be wholly and solely responsible for any damages and costs incurred by their delivery and any company equipment used in the completion of the customer's delivery, including but not limited to the drone crashing into a playground full of children." Just like Tesla's abrogation of responsibility when their "autopilot" software is driving the car they sold you...)
So while they gently introduce such rules (mostly centered around see and avoid for now, also identification), the main way they use to ensure safety is restrict where and who can fly them.
You know they can't be trusted, so you don't fly them above sensitive areas. As processes mature, reliability increase and trust is gained, you will see drones expand the airspace in which they are allowed. It's already happening for BVLOS (beyond visual line of sight) flights which requires a waiver from the FAA in the US (with paperwork such as risk assessment, collision tests on mannequins and so on), as well as specific equipment/processes.
Pretty much no one besides DJI has the scale for custom made, except on a few select components. Drones are still in their infancy, those companies are still trying to see if they have a business model and improving/creating technologies. You can't expect mature processes from this environment.
Problem is that most of the components (batteries, motor controllers, flight controllers) are built by and for hobbyists. Motor burns a winding? ESC spontaneously lets the smoke out? Whatever, they're $15 bucks each. The field of "commercial grade cargo multirotor" is still in its infancy. The balance of safety and cost for the components hasn't been struck in the market. You either deal with random chinese components and control algorithms written by intrepid RC airplane nuts, buy very expensive industrial/aerospace grade components, or roll your own solution.