Earlier quoted context omitted.
Perhaps the primary reason is accessibility. Onion addresses are not easily memorized. See https://en.wikipedia.org/wiki/Zooko%27s_triangle I believe this inconvenience is minor, however.
Incidentally, is there any fundamental reason why onion addresses are always so cryptic?
When you go to a website on the regular internet, the name you type into your URL bar doesn't contain any location information. Instead, you go to a Dynamic Name Server (DNS) server (often run by your ISP) and and get the IP address, which tells your browser where to go.
With Tor, the hashes you see are analogous to the IP in regular internet: they tell your browser where to go. But there's no DNS for Tor, so you can't hide address behind a name.
Incidentally, this story is about SciHub being blocked at the DNS level, meaning that the domain https://sci-hub.io/ was removed from the DNS servers. But it's still available at the IP level at https://31.184.194.81/
This story demonstrates the need for DNS to be decentralized. ICANN has far too much control and is now using it for censorship that holds back the progress of all of humanity.