Google, Microsoft, and Amazon's business model include selling compute - SpaceX, not so much.
Amazon is a bookseller and Google is just a web indexer. GCP didn't even open it's preview until 2008. Not sure why you think a business model is in any way a static thing.
Add Lidl to your list.
Why not? They can sell what makes sense for them, like surplus capacity, especially when there are desperate buyers.