I hope they're just too swamped to do it but the cynical part of me wonders if you're too far from any big poultry operations to bother with. You can get necropsies at a few universities if you're near one and really want to know. It might be cheaper than the vet would charge you. I don't know...
I think most people would accept depopulation of a flock that tested positive even if it is heartbreaking. The issue is that no one wants to lose a flock because it is assumed infected rather than proven infected.
Again, it can only work if they know where the outbreak is. People are already saying on here that they aren't going to be drawing attention to themselves which may mean they won't report birds that they observe dying in large numbers as one poster has suggested another should consider doing...
Having mandatory depopulation zones without testing is just asking for trouble. People will lose trust in APHIS and refuse to contact them. I personally would contact them if my birds started dropping dead as I'm the kind of person that has a mentality for the greater good and general respect...