So the author is paying far far less than the cheapest storage solution. So some folks may be selling surplus storage or free hard drive space for less than it is worth, but as soon as a system like this becomes popular the price will reach a much higher equilibrium.
Edit: I found packs of LTO6 tapes on ebay that worked out to be $4.30/tb, so less than an order of magnitude.
Here's my problems with Sia storage:
Time to setup and maintain contracts.
Confusion when it comes to type of contracts.
Big crypto files needed to connect with crypto network.
Unreliable availability of files.
Difficulty/complixity when trying to download your own files again when you want them.
I don't think Sia is a solution for the masses.
We agree with many of your points, and that's why we created Filebase[1]. We provide S3-compatible object storage at a fraction of the price and use Sia on our backend.