You don't have to look that deep to see the example.
Walmart categorically refuses to buy anything that runs on Amazon simply because amazon competes with walmart directly in retail.
having said that, i'm sure there are exceptions and some examples where they do have some stuff they use hosted on aws but that's the exception not the norm.
But yet Netflix is all in on Amazon even though Amazon Prime Video exists.
Apple depends on Samsung for many of its components and Google pays Apple billions a year to be the default search engine. Companies cooperate and compete with each other all the time.
They do, and in some cases or exceptions they bypass whatever internal rule they imposed on themselves just like your examples.
However, whether it's Amazon or another, it doesn't change the fact that businesses are in general averse to do business with a company that has shown in the past that it will enter a new market if it sees money in it at the cost of its partner relationship.
How many software companies have refused to run Windows because MS competes with them? How many OEMs went all in on Linux when MS started selling Surface computers?
