Either I pay the AWS tax or I pay the colo tax and either spend time doing netops or pay someone else to do. My hourly rate is much more than I would pay AWS to do the "undifferentiated heavy lifting" (https://joshlowryblog.com/2013/12/12/undifferentiated-heavy-...).
And there is the whole global infrastructure thing for regional redundancy.
I'm not saying its not worth it to use AWS (or GCE etc), but depending on your scale it can be quite exhorbitant, and you get quite dependent and coupled to those externally provided services.
You're always dependent on something. It's like the developers who use the repository pattern because they don't want to be dependent on Oracle/Sql Server, etc. Your entire enterprise is built on top of your infrastructure. You're not going to just change out to save a few dollars. The costs and the risks are too great.
And there is the whole global infrastructure thing for regional redundancy.