Bigger motor = more power? Not sure what the confusion is here.
Data Hoarder
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
Well if you are fan of random disconnects..
Some people go to Vagas to gamble. Some stay at home and gamble there instead.
Because 5TB has been the maximum for ages and isn‘t really all that useful
Speed and Capacity.
On your same logic, why use USB when you could just use a NAS instead? You don't have to plug anything in.
Well USB can only power a small mostly 2.5inch external drive and cannot really spin most large 3.5 inch drives.
And once you want larger sizes or more reliable enterprise drives which are in most large external usb drives you need power. If you are happy with a smaller ( and most likely less reliable ) 2.5 inch drive usb only is of course more convenient.
Actually USB-C could power it. Or at least some ports could. But USB-C is a clusterfuck hence…