If it was just one, I'd put it down to random bad luck. But with that many failures I assume they are doing something stupid/cheap.
Usually they would simply fail to power on but sometimes individual slots seemed to die (which RAID just loooooves).
And having an entire enclosure fail and waiting days/weeks for a replacement sucks as you lose access to all your data.
I eventually bought a Jonsbo N3 off of Aliexpress and PCI SATA card (to support more than the 2-4 drives most motherboards support) and that has been working well for months.