It would cost me $20,000 to transfer that amount of data over 3G, and almost ten times that on another common carrier. The amount of "cloud" storage is irrelevant in most countries.
WiFi....
An even more unfriendly prospect: at a typical Australian upload speed of 100kB/s, it would take 2982 hours (124.5 days) to upload enough data to fill the drive. At this point, most people would have given up and bought a laptop with a decent amount of storage.
I don't have to start paying a monthly charge on my HD to access my stuff after 3 years....
Instead you get to get to copy it over to your new machine, or forget and lose it. Convenience costs money.
But you very well might be replacing that hard drive after 3 years when it fails.
I need 1TB of fast storage, not on the other end of an internet connection, especially given that the cloud provider (or anyone that gains access to the cloud provider) can read my data.
I just calculated that I'd have to saturate my (normal-for-UK) ADSL uplink for 7 months to upload a terabyte.
I envy anyone who can actually make use of that.
... which you will pay your ISP out the nose to access.