I think politicians are much like managers in that apparently their job is not having any clue about how whatever they're managing works, but having a clue about how to herd human beings instead. And what is the single fundamental tenet of dealing with people? "Never take no for an answer", based on the observation that the surest way to get results is to assure the full involvement of your lab rat by forcing his interest to coincide with yours - ie. denying him the option to simply refuse what you ask. It turns out this approach more often than not produces results that are a workable compromise (for you the pragmatic tyrant) even when your original request is indeed a physical impossibility. It's all inconsequential - your minion, quivering in terror at the consequences of failing, will come up with something close enough.
Now, these days going medieval on your minions is somewhat frowned upon (to the great regret of the powers-that-be, no doubt), but the principle remains unchanged, which should go a long way towards helping us understand why they act as seemingly wilfully thick and stubborn as they do; it's not that they don't understand there's a fundamental problem with their request, but rather that us saying "no" just means they haven't put enough of the right kind of pressure on us. Coercion always gets results of one kind or another. No result just mean not enough coercion.
From the point of view of a techie thinking in absolutes, an imperfectly watertight, backdoored encryption is a useless thing not worth wasting any further brain cycles on. From their point of view, as long as they get their coveted back door, the rest of us getting left potentially naked in the cold is just a risk they're willing to take, even if they have to outright outlaw all "unlicensed" hard encryption to get there. I don't understand why we seem to think they'd finally "get it" if only we'd explain it all to them once again, clearly enough. Does anyone here seriously see these folks just going "oh, if it's not possible then of course just forget about the whole thing" at some point...? They DO GET IT just fine. As far as they're concerned, we're the ones failing to get it that there's no way out of this room until they get something approximating what they wanted...