Secrecy, shell corporations in particular, save them a lot of money before a data center is operational.
Once a data center is operational, it harbors significant trade secrets in terms of efficiency. Google is so frequently open because they stand to benefit from it. They don't benefit by lowering the cost of data centers for competitors, so it makes perfect sense for them to be secretive. They are secretive by default, and open when they reasonably believe they stand to benefit from it.
Google recently published a bunch of specs on their server fleet, touting energy efficiency. The designs were somewhat old, but certainly its not withholding information solely to keep data centers expensive.
Once a data center is operational, it harbors significant trade secrets in terms of efficiency. Google is so frequently open because they stand to benefit from it. They don't benefit by lowering the cost of data centers for competitors, so it makes perfect sense for them to be secretive. They are secretive by default, and open when they reasonably believe they stand to benefit from it.