Because adhering a readable graphical display onto the surface of a fingernail makes so much more sense than adhering it
literally anywhere else on your hand or arm.
Seriously, this is practically the very definition of technocrap. It's like in the Hitchhiker's Guide to The Galaxy, with the radio you control by making hand gestures in the air, with the added side effect that any errant minor motion will send the tuning hurtling across a dozen or so stations other than the one you were trying to listen to.
There is absolutely no reason to stick this sort of device on a human fingernail. In fact, there are some pretty good reasons not to do so, most of which involve the fact that the tips of your fingers are meant for touching things.
It's also not all that technologically impressive. This could be produced with current technology today, and it'd STILL just be a gimmick. Show me a HUD in my glasses or implanted in the eye itself and I
might be curious. And even that won't take 150 years to perfect.
This is just one massive malaise of marketing masturbation - the sort of visionless pap that you get when you ask corporate drones to envision a product to fit a "futuristic" aesthetic.
~Umi