Why Nexus 5X take high resolution photos in 4:3 aspect ratio rather than 16:9 ?

I like photos to be taken in 16:9 aspect ratio as you can view them on full screen of mobile and can see details of photos . Galaxy s5 had 16 mega pixel camera taking photos in 16:9 ratio why nexus 5x camera allow 16:9 aspect ratio only in 8 mega pixel while aspect ratio is 4.3 when you go for taking photo sin maximum resolution? Is this restriction from native camera or camera application? I also hate google camera app of nexus 5x which has very limited options and ugly design..even when you take photo in 16.9 ratio they have black bars restrict the views unlike samsung, sony camera app where you can see viewfinder on all screen?

can anyone suggest some camera app which are as good as sony/Samsung/htc built in camera app and also if its possible to take photo in maximum resolution in 16: 9 aspect ratio,,thanks

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