The answer is - these are not core office buildings for those F500's. They want capitally efficient (e.g. minimal up front investment), fast to market and appealing to a desired workforce. GE wanting to set up a R&D center to hire 100x 25-40 year old developers in Austin? Great model. When we hit a recession, those are the first jobs to go and then they have preferable (e.g. not left sitting with the asset) ways of winding those centers down if needed.

Think of it like having 3-year Reserved Instances in AWS instead buying your own hardware and running your own data center. Which would you choose today?