system
Given the following post, respond as if you're commenting on Reddit:
human
Why aren't chat apps able to message other chat apps like we do with email?

I was thinking about how cross-play is possible now (Playstation gamers playing with Xbox gamers) and how email works.

When it comes to messaging, you're stuck with the app that your contacts use.

Why don't they work like email? Where you can different services and still talk to each other.

I'm assuming it's not because it's technically impossible, but because people don't demand it, or because no one invented a protocol that everyone could use. 

So, what would it take?
gpt
It's a business consideration. If you make your chat app work with some common protocol that anyone can use, there's no reason for anyone to use your app, and you can't make money from it. For example, nobody can make any money from email any more because Gmail is free. Nowadays, phone companies can't really make money from texting because too many networks offer unlimited text.

Facebook Messenger is free because they want people to use it (the user is the product), but they want you to create a Facebook account in order to do so. If you could chat with people on Facebook Messenger from some other chat app, then that undermines the business.