Real estate transaction costs can be huge, IF the rent is reasonable (apparently not this case) then paying rent on underused space is basically a real estate options market. There is a viable business model here, its like insurance that if you need an additional long term office next Monday, just walk in to "your" space. It might be cheaper to make one transaction, pay your 6% or more of commissions and fees, underuse the space, than to pay two 6% commissions and fees (and labor to do the second deal).
Several employers ago I got to learn about financial industry disaster recovery plans and you'd be surprised how many traders have an empty office squirreled away on the other side of the city as their tornado/fire recovery plan. Sure only 1/20th the employees would fit, but its only 5% the rental cost of the real office and some bean counter said that was an acceptable loss to provision an office with no people and a stack of server hardware. If they let people work from the D.R. site that would be a public admission that people don't need to work in a bullpen and could just as well work from starbucks or home, but that would not meet the emotional need to intimidate people in person and demonstrate butts-in-seats metric goals so using the D.R. space for actual work would be unthinkable unless the main office was literally on fire.
This combines with open office style, such that people can't avoid noticing unused space, although unused space is hardly a new feature of the business world. There's a small room right down the hall from me, but its behind a locked door, so no one notices. If they were not an open office company, they'd just lock a door and no one would notice. Placing their capacity on display like this is arguably an architectural design fail, they should have found an architectural way to "hide" empty space from casual visitors in an attractive and cheap manner.