Thin disk faster then thick eager zeroed

Hi,

any one can explain me why thin disk works faster then thick eager zeroed on same datastore ?

THIN:

fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test --filename=test --bs=4k --iodepth=64 --size=4G --readwrite=randrw --rwmixread=75

Jobs: 1 (f=1): [m(1)] [100.0% done] [284.3MB/96892KB/0KB /s] [72.8K/24.3K/0 iops] [eta 00m:00s]

test: (groupid=0, jobs=1): err= 0: pid=4133: Sun Jul 16 22:27:32 2017

  read : io=3071.7MB, bw=289577KB/s, iops=72394, runt= 10862msec

  write: io=1024.4MB, bw=96567KB/s, iops=24141, runt= 10862msec

THICK:

  read : io=3071.7MB, bw=172067KB/s, iops=43016, runt= 18280msec

  write: io=1024.4MB, bw=57381KB/s, iops=14345, runt= 18280msec

What a mystic?

Datastore located on 4x SSD, RAID: 0, VMFS6, ESXI 6.5