You aren't getting the point of a connected drive. The point is that it is hosted in a data center, so you can actually share the data easily, over internet. Also, I believe they use OpenStack Swift as a backend (just like many others), so then your data are stored 3 times in a distributed system. That's a way safer than RAID-1 or ZFS. Sure, you may use Swift at home too. But would you run 3 servers ? The cost of electricity makes it then in the advantage of the cloud provider offer, than is having hundreds of servers shared between many customers.
FIY, at my $job, we are now standardizing on 16x 22TB HDD servers, and push 6 servers at a time on our clusters, because 6 availability zone, and 3 regions (2 data centers) to make it safer. That's very different approach from a small NAS...