The problem is just a presentation one.

Email is thought of as grandpas business tool.

Look at Spike for IOS.

Messengers are just whitelisted users. Email providers or clients simply provide a shit interface for managing that list.

To me it’s like that story about NASA spending millions on a zero gravity pen when Russian astronauts just used pencil.

Someone was looking to impress people with their spam filtering code and never thought “maybe I can just drop all by default and only allow who I want?”