From the perspective of a business, building your own data center only makes sense if it part of your business (like at Dropbox). Paying a margin for a service that is not part of your core model is per se not a bad thing, in most cases it makes a lot of sense. That is because if a company makes a huge investment, it makes this investment with its own capital. In theory (and that often applies to reality) a company can only invest money effectively in its core business.

This is why many companies with a lot of money still rent their offices – even if they intend to stay in the (often customized) buildings so they don't need flexibility. It just would not make sense to buy and to bind the capital in a building, it can be invested in their core business with higher returns.

An exception might be made in cases where a company has suddenly so much money that investing it all in its core business might diminish the capital/return rate, eg. through the US tax break, where a company shifts the money stored oversee back to the US. This is why for Google it might make sense to buy property, even though its not their business: They just have to much money.