Metric uses weight in many cases where imperial uses volume. This makes the translation of old recipes into metric a chore. And it means you need a kitchen scale, something that a lot of of good cooks manage without in the US.

There are other barriers -- no one is going to replace their oven just because the numbers on the temperature knob don't match a new recipe (they might buy a new knob if it was easy enough, though!).

All in all, the arguments for not going to metric across the board is the same old "we'd rather have our kids deal with it". But fubarobfusco is correct, it is unlikely that it will happen in the next decade or so. The market clearly won't demand or accept it.