In theory, I see what you're saying. In practice, I've only ever seen Amazon get into a spat with Google, when at one point the Firesticks did not offer YouTube or YouTube TV. But that was years ago.
As I understand it, Prime Video is a loss leader itself for Prime subscriptions and Amazon (Bezos) has viewed it as somewhat of a vanity project. If so, that would explain to me why the Fire products have never ditched Hulu, Netflix, Max, Disney+, etc. To the contrary, I believe, you can get all those things as add-ons with your Prime subscription for the exact same price, so they have seemed to be committed as a platform and not just a funnel for their own streaming service.
I do wonder if that's changing, or will change. I notice that regular Amazon Prime subscriptions only gets you Prime Video content with commercials now. If you want to drop the commercials you have to pay extra.