Because Apple isn't making a single watch that will even fit my wrist. I'm a big guy, no doubt. I've got quite a bit of muscle, and then I'm a bit overweight on top of that muscle, but still: my wrist is 223mm in the spot where I'd wear a watch. It's 203mm at the narrowest point right at the joint, so, technically I could get one on my wrist. However, being right at the joint, it'd be incredibly uncomfortable to wear when doing anything except letting my arm hang straight. When I wear a watch, I always put the edge of the face at the joint so that when I bend my wrists it doesn't dig into the watch.
Why such restricted sizing on these bands?