Comment by tgsovlerkhgsel

As soon as you do that though, it becomes a nightmare to adjust anything about the protocol, and you end up with incompatible clients. So you can use the app perfectly with friend 1 that has the official app, but with friend 2 who uses one client, sending photos doesn't work, and with friend 3 voice calls don't work, and adding friend 4 to a group chat somehow breaks it entirely for everyone.

Friend 2 insists on using their client because it has dark mode, and for the average user, what they see isn't "friend 2 is extra and has a broken client", they see "that app fails to send pictures about a quarter of the time, let's use whatsapp".