I don't think it's cost cutting - the price of office space is far outweighed by knowledge worker salaries. I think it's a whole range of factors, but the largest is this: when a tech company becomes successful, they grow fast and are too busy to do a search for a proper office. So you see a lot of successful tech companies with tight, open layouts. Then you simply confuse causation and correlation and say "oh it must be their cross team communication!"