Because you flex and replug the interface often.

The thing you use to plug your phone, tablet, drives and other things with is very often the failure point unless you break screens or get water in them.

Normally you simply have a HDD drive with a SATA interface in there, so if the USB connector fails, you can still easily recover your data.

With these things, you're lucky if they even offer the possibility of repairing or recovering the drive.