Question Why no USB 3.0 to PCIE exist?

[ProDigit10]

Hi,

I'm using my PC for folding.
Folding doesn't use a lot of PCIE bandwidth.
Is there a reason why there are no USB 3.0 to PCIE 16x slots available?

I realize that a USB 3.0 is about 1/2 the speed of a PCIE 1x slot, but that might just work on a GT 1030 card externally for folding!

 

[CountMike]

All PCIe cards fit into x16 slots.