[robjan]

The problem is when one friend demands Signal, another WhatsApp, another Matrix, another Telegram, another Threema. These are all closed platforms and having loads of different apps installed which perform similar functions，to satisfy various people's dogmatic views is annoying.

[vurpo]

Matrix is not a closed platform, and in fact the only one of the projects you mentioned that even makes an attempt to work together with other chat protocols and networks. It is explicitly open, not locked in to any single service provider, and making an explicit effort to not limit you to chat with only other Matrix users (despite how much Signal or WhatsApp works towards the opposite).