What did 2TB of SATA diskspace cost 5 years ago? What does it cost now?
What did 4TB of SSD diskspace in HARDWARE RAID 10 cost 5 years ago? What does it cost now?
Same with CPU's. They manage to make newer faster ones making the older ones more affordable etc. Hardware and networks get cheaper and cheaper, but resources are squeezed more and more, either way, e.g providers may offer better specs but put more customers on the beefier servers because of it which is the same as less beefy servers with fewer customers on it.
The main thing that costs money is labour/admin time, and by offering so-called "unlimited disk space" for peanuts, it will eventually catch up with them (think EIG). That is the case when a large number of customer's abusing their service by uploading around 1TB of data for $1.99/month and who are probably the type of customer's submitting 50 tickets a month.
In the end, you get what you pay for, and while you might get a great offer to start with, it most likely will not last if the offer is too good to be true.