[vacri]

at $600/month you've only saved them $1500/month (the hosting portion is only $2.1k), and now they also have physical hardware to manage, requiring a broader skillset from the volunteers, plus someone having to be in physical proximity for 'on-call' issues.

I don't know what datacentres tend to charge for data transfer, but as that's the largest item on the bill, it's the more salient point.

Also, just because it's not on the bill doesn't mean they're not using other AWS services; there are several free ones.