Why aren't there screw-threads inside the Aeropress sleeve?

I'm staying in a hotel with nothing but paper cups in the room, and I'm not travelling with my usual suitcase in which I stash my emergency polypropelene folding cup, so I'm reduced to making my hotel coffee using the awkward hold-the-sleeve method, in which you grip the sleeve as hard as you can with your left hand while pushing down on the piston with your right, supporting the press so you don't crush the paper cup beneath. (more")