Probably the advantages of its location outweigh the extra costs for the IA. Having your datacentre sited on land and in a building you own, behind a non-shared front door, has legal advantages similar to the ones which drive organisations to keep their data centres on-premises. A distinctive location in a nice area of San Francisco probably helps to keep cultivating the goodwill of the SV tech industry and of local and state politicians. It's also an advantage to be within easy walking distance in a neighbourhood where people like the IA and would be inclined to go there and protest if government forces rolled up and started pushing their way inside. To be sure, I presume that 300 Funston Ave. also being a very pleasant workplace for senior IA people has something to do with why the Archive moved there and remains there; but remaining there seems justifiable for other reasons.