Comment by lioeters

> What will Apple gain from making it ubiquitous?

Right, I'm trying to understand Apple's motivations, and this question applies not only to iMessage but their general approach regarding macOS, apps, app store, the proprietary/locked-down nature of their software and hardware.

The opposite of ubiquity would be "exclusivity" - and that does explain a lot. The reasoning must be that there is value in making their apps exclusive to their own OS(es). The same way you can't (easily) run macOS on any old PC, or the way their hardware doesn't allow users to repair or extend it.