I could understand if there was really an overlap somewhere, but I don't really see it. They have different business models, Apple doesn't have any social media property that compete with Facebook or Instagram and if Apple really wanted iMessage to crush WhatsApp they should at least show their interest in dominance by having an Android version of it.
Maybe they are competing on resources? but I don't see it either. They don't seem to be going after the same acquisitions.
Maybe Apple is doing this because pleasing or pissing off ad-based companies has no effect on their bottom line and they see it as a good marketing campaign to woo the privacy conscious an earn some brownie points for practically zero expense.