Why is is this not possible?

Hey guys,
I have been doing doing alot of reading regarding eGPU's and I find the idea fascinating. I have seen many people using the PE4H with the Sonnet thunderbolt express card adapter . Some criticism is the express card bottlenecks the connection at 5 Gb/s instead of thunderbolt's 10 Gb/s, but I have still seen some impressive performance gains with it regardless. What I am wondering is why it can't be done with USB 3.0 which is capable of 5 Gb/s instead of thunder bolt. Since the speed of USB 3.0 is the same as the bottleneck shouldn't the gains be on par with the thunderbolt set up but cheaper and more widely usable? I did some digging and was wondering if the PE4H could be used with this Expresscard to USB 3.0 Adapter? I haven't seen it done before which makes me think there is a major flaw with this thinking and I was wondering what that might be?

 

I heard it was mostly drivers. Besides native thunderbolt solutions are 10Gb/s per lane.
http://forum.notebookreview.com/e-gpu-external-graphics-discussion/662462-usb-3-0-solution-yet.html
http://www.imore.com/usb-31-spec-finalized-will-match-thunderbolt-1-speeds

 

you also have the base characteristics of usb, its crap for any continuous information exchange that needs quality and stability