Messaging apps, like social media services need your friends to be on the platform for it to be useful. If you start putting friction into that process then the services are instantly not useful. Everyone of your friends that doesn't join makes that thing much less useful for you.
You say "everyone" is willing to pay that. I'll tell people about an amazing app that solves their problems they are complaining about and they go and see it's a couple dollars (one time purchase) and still complain and usually don't buy it.
There will never be a popular messaging service or social network that relies on subscriptions (maybe subscriptions for additional features though)