My opinion on the matter.
1. What would you imagine they could do? Beyond calling tech support.
2. They do host their own website. But if you have more traffic than a very small company, "hosting" yourself would equate to having a cloud service. Next you ask, if they can't have their own power plants, instead of dealing with the power companies.
And yes, bigger companies actually do just create their own cloud - and promptly rent it out to others. Find out, what aws stands for. And with solar roofing and such, many companies do create partially their own power, but I am not aware, if a company created their own power company.
3. Steam and Google have a lot more redundancy and backup systems.