The One Big App To Solve All Problems is the wrong way to go, in my opinion. From a coding standpoint, it's a maintenance nightmare. From a UI standpoint, it's nearly impossible to create something that is both easy to use and comprehensively granular. From a user standpoint, it's confusing as hell when that "one thing" doesn't work like it's supposed to.

Yeah, you're right in the sense of why do we need all this stuff? The answer is: because no one uses just one thing to communicate.

On a slightly different note: if someone messages you and is expecting a response, do you really need to try three or four different methods to send that response? Shouldn't the expectation be that you would send a response back by the method that they made the request?