It means that even if you still use the default iOS messaging app, your contacts can use other messaging apps, rather than being locked into iMessage and therefore the Apple ecosystem. It breaks down some of the barriers to competition for new mobile OSes and messaging apps. This is a good thing.

Yeah, I have been effectively banned from video chatting with my family, since they all use FaceTime.

Because some users might like a different messaging app better than the default one?

Messages are big in the US. But in Europe I've seen people using anything but Messages.

So Europe will happily continue using other messengers, but now in a more interoperable way, hopefully.

The comment you’re replying to is about app stores, not messaging.