Amazon did it a long time ago, and when they started, they had no sales team. They had to build that capability slowly over time, but they had the first mover advantage, so they had time to learn. Now they are number one.
Microsoft already had the enterprise sales team, they had to learn how to sell cloud. They had some trouble with the shift, and with the technology, but now they are knocking it out of the park, and are solidly in the number two spot behind Amazon.
Google is struggling with their cloud business. While what they offer is technically superior to all their competitors, they don’t have the sales team, nor the experience in building one. They are trying, but they haven’t gotten the hang of it yet, and in the meantime, Amazon and Microsoft just keep growing.
This is the position Facebook would be in. They probably have the technology, or can at least attract the necessary talent to build it (I know that I would at least listen if they said, “Come build a new cloud with us from the ground up”). But they don’t have the enterprise sales team, just like Google.
Now, in Google’s defense, they have realized they are coming from behind, and as such have focused on selling their higher level services. If you want to do AI and Machine Learning, Google’s cloud is the place to do it! And then maybe while you’re there, if your core business is AI, maybe you’ll use some of their other services as well, since your data is already there.
Facebook could make a similar play. They could build a cloud and then require any 3rd party apps that work with Facebook to use their cloud. This would jumpstart their adoption, and could potentially help them solve their privacy issues. They could require that you never send any personal Facebook data out of their cloud, and could closely monitor all the outbound traffic. Then they could theoretically allow even more access to Facebook data, if they knew they could control what happens to that data after the 3rd party gets hold of it.
In other words they could launch a cloud that lets you run your 3rd party Facebook apps in a controlled and audited way, and even give you building blocks to do it quickly and efficiently. It would boost their bottom line, because there is good margins in compute and storage, and at the same time give them more control of their own data.