This just doesn’t make sense. Google/Amazon employees basically are some random DevOps “dudes”. Whereas your own people would be...whoever you decided to hire to work on your infrastructure.
Problem being that Infrastructure is made to be very, very compicated because they're selling tons of managed features that have reliance upon each other. I don't know why this idea of having your own devops is suddenly now bad. renting your own bare hardware and managing solutions yourself is still very much a thing and something you have to do if you're using lots of bandwidth. Dropbox for example made their own infrastructure to get off of AWS [1].
I don't think that anyone thinks having your own infrastructure is bad, or if they do, they likely don't have much experience. Rather, I think it can be a nightmare if it's not properly managed, and it's hard to develop the skill to properly manage the process unless you've been burned in the past.
It's like an insurance. You wouldn't be able to hire as many and as highly paid random DevOps on your own. So you and others pay a 3th person to do it, just in case you need a competent person.
Hiring some dude won't give you that.