[stuporglue]

For 1:1 conversations I think you're right. Having multiple channels for communication is fine.

Where it breaks down is for group conversations. If Person A won't use Signal and Person B won't use WhatsApp, you can't easily have group communications. And it only gets worse as the number of people in the group goes up.

[palata]

In my experience, people who use Signal usually also have WhatsApp. It's really mostly that many people absolutely refuse to install Signal on their phone. Like they have all sorts of apps (including social networks that are sometimes downright malware), but they will fight against Signal for some reason I don't understand.

[oqy]

The reason is simple: Comfort. They simply prefer not to have the mental load of multiple channels, albeit at some cost.

That's the appeal of software like Beeper&Co.