"On one hand you have hard data, open offices cost x, open plan costs x/2, on the other hand you have "engineers say they could be more productive with offices" against "do you remember when we were small and working in a single room, that was awesome, we were so agile and communicative" (whether or not that is applicable at your particular company size or stage, burning the midnight oil on your stack to cobble together a demo for a pitch is not the same as writing production level tricky security code)"

Not to mention that part of why you do that then is so you don't have to do that anymore.