Both your Filecoin and Golem examples might be inexpensive but they have no sort of SLA for end users. They can also evaporate tomorrow taking your data and compute resources down with them. Both systems are only viable if the cost to run the systems is below the money made from running it. If the whole reason users pick Filecoin is the price, they'll abandon the platform if the price ever increases (to make running nodes profitable) which creates a feedback loop that will collapse the network.

While Amazon might cost more, they're unlikely to go out of business tomorrow or in ten years. They also have an SLA and predictable prices and predictable capacity. if you build something on AWS that works today it'll likely work tomorrow.