Glucose is also the lowest calorie way to treat it - no additional calories in the form of fat/protein/etc (e.g. if you used chocolate, which is not ideal anyway as it's much slower to be broken down and absorbed).
Glucose is also better than sucrose (plain sugar) - glucose is absorbed directly in the mouth and stomach and the full quantity is of immediate use. Sucrose must be broken down by an enzyme into glucose + fructose. This is a fast process and also occurs in the mouth and stomach (where the glucose component can then be absorbed directly), but this leaves the fructose to be absorbed more slowly further down the digestive tract, but which point you probably won't be hypo any more and therefore these calories are not useful.
Edit: I've since looked into this further and it appears that sucrose isn't broken down in the mouth and that the enzymes are released by the small intestine, so I've crossed out my comment above - this is interesting as you can get a fairly quick recovery from a hypo by eating plain sugar, which means that no matter what you've previously eaten at least some of that sucrose still makes it to the small intestine quite quickly (where it is broken down and the glucose and fructose are absorbed) - I need to look into this more because I'd always assumed that eating things with fat (e.g. pizza) simply slowed transit which meant the carbs didn't get to the absorption site as quickly, but apparently this can't be true. The premise above still holds true though, glucose is the lowest carb (and fastest) way of treating a hypo.