One of the reasons the video streaming services work so well is that they use global Content Delivery Networks to locate their read-only content near to their users. That is probably cost-prohibitive for SUF which is why they have a downloading option.
Data centers have outages, you can mitigate them with good design, but that requires a lot of money and is not a sure solution.
In addition, if your Internet bandwidth maxes out, or worse, local conditions such as traffic demand cause slow downs, nobody in the universe can solve the problem. Remember when Michael Jackson died, or on 9/11 how everyone’s Internet degraded.
This is a problem with distributed computing that will never go away.
Connectivity is never guaranteed, you should never assume that you are always connected.
I could go into a long discussion about resource contention, the speed of light, Shannon’s Law for bandwidth capacity, network latency, and failure-based architectures, but I doubt it would matter.