Why was it uselessly slow from a USB 3 flash drive?

[Fiksdal]

I did a benchmark of both my USB 3 flash drive, and the old, mechanical, spinning drive. It looks like the USB 3 flash drive performs much better, even when it comes to 4k read write. So why is it so hopeless to run Windows from it, then?

Here is the old USB spinning drive ( the one I'm currently running Windows from.)

Microsoft Virtual Disk 136GB
(9 User benchmarks - Rank 170 - Average bench 58%)
96GB free
Firmware: 1.0
SYSTEM 4KALIGNED
Performing way below expectations (5th percentile)
Rank 931
16.7%
Read 30.9
Write 26.9
Mixed 9.81
16% 22.5 MB/s
4K Read 0.31
4K Write 1.39
4K Mixed 0.22
64% 0.64 MB/s


Here is the USB 3 flash drive that Windows ran terribly slow from:


SanDisk Ultra USB 3.0 32GB-$9
(962 User benchmarks - Rank 121 - Average bench 26%)
24GB free, PID 5581
Operating at USB 3.0 Speed
Performing way above expectations (98th percentile)
Rank 29
40.6%
Read 140
Write 59.7
Mixed 26.5
77% 75.3 MB/s
4K Read 4.39
4K Write 2.03
4K Mixed 1.24
127% 2.55 MB/s


Here are the full results: http://www.userbenchmark.com/UserRun/1002256

So why did the USB 3 flash drive perform better in every way on the test? Yet, Windows runs just fine from the spinning USB drive, but terribly from the flash drive? Why is this?