The main reason UWP exists is to make cross-platform (*Windows 10* cross platform) development easier. And it makes perfect sense from an apps point of view. I'm running exactly the same Netflix app from the Windows store on Windows 10 as I would if I owned a Windows Phone, or Surface, or Xbox. Netflix have only had to develop a single app which can be used on all devices. This is a huge bonus for developers - if a bug is found in the app then they only have to fix it once rather than fixing multiple versions for multiple devices and rolling them out separately.
The gaming area is a little more muddy. There are games which will benefit from this same write-once-target-many approach (such as the Windows 10 version of Minecraft) but the benefit to games which are only going to be released on PC is questionable.
However, it does mean that it's attracting games which we would have never previously got on the PC, such as Forza and Halo. I don't care if this is a result of developers liking UWP, or if Microsoft are incentivising them - I think these games on the PC is a good thing.