They don’t have any infrastructure themselves, the game runs on aws, buying a petabyte of fast storage on aws doesn’t sound cheap. But I haven’t actually checked the prices. 2k players sounds also quite low. They also can’t really compress the data if it has to be accessed with low latency, on top of that I think aws cold storage had a delay of 30-60 seconds when retrieving the data so the cheap petabytes won’t work here.
I’m not saying that it’d be impossibly expensive, but there is a cost.
edit: Yup I don’t think glacier would do the job here 
edit2: Don’t take this as an objection, we’re actually on the same side, here’s my post about storing the items and the storage concerns that came up