Turns out local (Swiss) regulations prohibited a food delivery van to carry both refrigerated fresh food and unrefrigerated, dirty containers at the same time.
The company really wanted to push towards reusable containers, but that would legally require making two trips, so it could never be economical.
When we order food deliveries, there's usually an option to specify how many set of utensils we want. We specify zero. If there's no option, we write something similar in the 'notes' section.
These instructions are almost always ignored. I guess it's cheaper for them to add utensils in every order, than to spend time to read the specifics of each order.
The platforms themselves may have good intentions, but it's not reasonable to expect them to enforce that with restaurants. I mean, if restaurants want to give customers stuff for free, and customers don't complain, then it's hard to blame the platform.
Consider this: in the US and UK, sales tax (or VAT) is mostly enforced via the threat of a random audit. In China, official receipts can only be issued on government-issued stationery, printed using computers that are connected to the tax bureau. The threat of random audits is too weak, and open to corruption and uneven enforcement.
Perhaps permanent containers could be used for food delivery charges on a deposit basis (pay money for them, get it back when they are returned, perhaps sent back on a future delivery).