Indeed. "Cloud" is essentially tons of commodity hardware nodes running a tailored userspace distributed file system application. There now certainly exist cloud services that host well in excess of 2^64 bytes, but they are not hosted on traditional file systems, but an array of those.

I can't certainly blame their choice though, and 16-million terabyte hard drive arrays (the limit of 64-bit addressing) on a large mainframe are really just a few quantum leaps away. Heck, I still vividly recall buying a MASSIVE 40 GB HDD in 2000 - it seemed excessive beyond wildest dreams at the time (and was promptly filled to brim at a LAN party.)

Since, advances in mass storage tech, most importantly the successful commercialization of perpendicular recording in 2005, mean that nowadays 12 TB drives are commercially viable - roughly 1000x the size of a 40 GB drive.

In the next 20 years, petabyte-sized drives might well be available (though almost certainly not based on any form of magnetic recording). Once you hook hundred 50-petabyte drives to a single fileserver, you start closing in on limitations of 64-bit addressing.