I had a chunk of credit to spend on GCP, and it's been much better, and seems to be about the same price. (We went with AWS at work because, at the time, it was simply cheaper for us).
What would be interesting though is infrastructure that leans on what they know best in terms of architecture and development.
GraphQL APIs, React frontends, PHP, JS, MySQL... Stuff that works for them is widely adopted by the webdev world as well and webdevs want convenient, scalable infrastructure.
Oh and they also have people working with/on Haskell right? I bet tons of Haskell devs would love use FB infrastructure if Haskell support was provided. A niche market for sure, but I suspect it is one that longs for something like this.
The industry is closer to large airplane manufacturers (e.g. only Airbus and Boeing), search engines (Google and a little bit of Bing), and similar.
Shoes, jam, and hosting services all require minimal investment. (Cars require a lot of investment too, but not at the level of building a cloud. Which is why there are more than 4 brands of cars, but not 4,000 like shoes or hosting services.)
EDIT: In response to comments below, I'm not talking about physical infrastructure here, which does scale rather than being largely up-front. I'm talking about the absolutely massive software investment in tooling and reliability. Not only are you building 1,000's of API endpoints across dozens of services, but you need to also guarantee 99.99% uptime and virtually zero data loss when required. And sure, a company like Facebook is the type of company that can engineer that stuff -- but it still costs $$$$$$$$$$$$ to build.
Citation needed. If anything, it's the opposite, it scales up very linearly.