Well, they do, within limits. That is, if you want a very short length, you adjust the angle to almost zero, and push it way down into the steerer tube. If you want a long length, you adjust it so the stem part is parallel with the ground.

I used mine to find just the right position, then bought a regular stem. The adjustable tended to become loose, and creaked when climbing hills standing up.BikeNewTires 002.jpg