Re: "they eventually simply stopped responding entirely"
Surely there must be someone at D-Link who is aware that they now have an impending PR scandal coming their way
I'm sure everyone in software engineering knows but they need to balance this with "how much will it cost to fix". This sort of behaviour is the new "norm". And it will continue to be unpatched until some big ISP announces a boycott.
Take the example of Boeing 737 MAX and the FAA: FAA dragged their feet and refuses to issue a critical advisory. It took China's aviation regulatory agency decision to ground the class (of aircraft) before FAA, reluctantly, followed suit. And the rest, as they all say, is history.