It's mostly about power. To use some USB hub with most USB POWERED HDDs means it won't work unless you are very lucky and the USB HUB HAS ITS OWN POWER SUPPLY.

Now if the USB DRIVE is SSD or a STICK you usually find that works but the USB HDDs for decades draw about the maximum that the USB port allows so the usual USB HUB that uses USB PORT POWER should fail.

Not much mystery here.