One big reason I believe would be price.  Also very easy to put new gear that is nothing special in aircooled data centers.

I think it is going to be very very hard to beat a data center that can do evaporation cooling.  That is huge being able to do that large scale.  Other option is putting ton's of CFM of fan's and exhust it out.

I think price is reasons that site does now show a real unit just rendering of what it could do.  It's been a long time but there was one that had a immersion based at decent scale I believe, but it was a good while back.  Like asicminer blade days.