Because let’s be real…clients don’t have titans X, Oculus rifts, gamepads and toys like that!
I recently discovered rendertargetcube (360 image of your scene) in unreal and used it in a 360 viewer app on the net. You can explore it/zoom but just can’t move.
It’s nice for low spec computers, ipads, iphone…etc. I exported the rendertargetcube in .hdr and changed it to .jpg in photoshop. Then I uploaded it on this little vewer app.
http://panoramaviewer.1bestlink.net/
Here’s a video of my scene in the viewer (resolution is 2048x2048 from unreal, but I’ve heard there are ways to raise it even more)
It’s a test, viewport quality wasn’t that great when I took the rendertargetcube.
Compare this to vray where it takes a long time to render that kind of image, with unreal it’s instant 
Now just need to find a better app, perhaps on appstore or google store!!!