Earlier quoted context omitted.
Bandwidth is effectively free for many users (no data cap), and the amount of processing power required for something simple like file storage is pretty trivial. You're right that it's non-zero, but I'd imagine it's probably on the order of pennies a month.
Is it really? Even just extra 10W over a month is just under 7 kWh and might approach a dollar[1]. Spinning 3.5" HDDs from time to time is especially costly and they often spin down when unused for a long time. Load spike might also make CPU freq scale up and consume more power. Same with bandwidth, you'll incur ISP wrath or saturate it (or keep wasting most of that free space), even 80 Mbps[1] is 'just' 36 GB / hour…
It's worth noting though that Sia (another decentralized storage network) is estimating their current storage costs at $2/TB-Month. That's half the price of Amazon Glacier. Whether that's the result of users farming from their home PCs or giant Chinese storage farms though I have no clue.