How to identify the cause of slowness of an external hard disk?

I have 2 Weste Digital exteal hard drives, namely:

I coect them to my laptop (MSI G Series GE70 0ND-033US 17.3-Inch Laptop (Black/Red)), which runs Windows 7 SP1 x64 Ultimate.

The 2 Weste Digital exteal hard drives are slow, and I don't understand why. I tried two different USB cables, and two different USB ports. All USB cables and USB ports are USB 3

Below are some CrystalDiskMark benchmarks:

WD My Passport Ultra with USB cable 1 USB port 1 (both USB cable and USB port are USB 3):

WD Elements with USB cable 1 on USB port 1 (both USB cable and USB port are USB 3):

WD Elements with USB cable 2 USB port 1 (both USB cable and USB port are USB 3):

WD Elements with USB cable 2 USB port 2 (both USB cable and USB port are USB 3):

In theory, everything is USB 3: the EHD, the cable, and the computer's USB port. According to HD Tune, both EHD are healthy.

What could explain the slowness of the exteal hard drives?