Because whoever has stolen them has been reasonably discreet, and we don’t see compromised Apple things all over the place — which means if they’ve been stolen at all, it’s been by high class attackers.
If your goal is to stop the NSA et al stealing a key or owning a device, you’ll be sad.
But if your goal is to change the law and redefine the parameters of them owning devices, you might make progress. The political process will insist on a means to access these devices, and they’ll accomplish it by one means or another. By engaging with instead of fighting that, we gain the ability to have a say on what those means are.
How do you know that?