I'm disappointed WhatsApp became the defacto solution for secure communication. I am also disappointed Signal became the defacto alternative. I also think Matrix is a better solution and I'm rooting for it. But I think your response is unreasonably pessimistic and, frankly, arrogant.
For all its problems, WhatsApp was an improvement to the status quo. User messages went from being fully public to only being accessible by Facebook. Signal was also an improvement. User messages were finally encrypted from end-to-end, even though Signal retained control of the infrastructure and kept some of it opaque. Things are improving and there is no reason to believe Signal will have any more staying power than WhatsApp or any other platform.
As for why Signal beat out Matrix, I think the technical hurdles are a relatively minor factor. After all, signing up with Element doesn't require hardly any technical understanding. I think Signal was just a better known brand with a larger established userbase, streamlined on-boarding process, and ubiquitous feature support across many platforms.
I don't think it's appropriate to call Signal's users or the techies who recommended it "stupid". I think most of them just realized a communication platform is only valuable if the people you communicate with actually use it and that Signal would be an easier short-term sell. I think the chaps at Element realize that and are trying to position themselves as the next logical alternative once Signal eventually has its own mass-exodus.
There is still hope for Matrix. Just keep championing it and show some patience to your fellow human.