Because it looks nice the way it look in the preview. If I wanted the final thing I would have waited for it and made the switch from Maxthon to Project Spartan...
EDIT 02-Apr-2015: Now that an official Windows 10 build with Spartan has been publicly released, it would be nice to see someone make a skin Don't get me wrong, having the real deal is awesome, but Maxthon has sooooo much more functionality