They're a lot harder to build out from those sources because they are costed to run 24/7 and the intermittency issue comes to the fore. Unlike things like aluminium smelters there isn't always a good load-shed or even supply-timing story in a DC, cooling aside (big chunks of cooling can be used for demand management)

I am not in the DC business. if somebody who is says "thats bunkum" I'd pay attention to it.