To make it flat like you're talking about, you'd have to add a lot of excess material. What I mean is, everything is round. The reflector is round, the lens is round, and the batteries inside the body are round. For it to not be round, you'd have to add size to the light. You can't simply flatten two sides of it because you'd be cutting into the body. As it is now, round, there's a minimal amount of material, yet it's still structurally strong. Adding material to make it "flat" would mean more material costs and probably manufacturing costs, not to mention additional weight.
That's one reason I like lights with pocket clips so much. Besides making them easier to carry (in the pocket), the clip acts as an anti-roll device. As for the L2T, you could probably rig up a thingy out of paracord or rubber to prevent it from rolling.