I think because simpleX is more open source, self-hosted, and maybe slightly more anonymous. Not sure how the usability trades off for that if at all because I haven’t used it (I mainly use signal and discord)
It also doesn’t seem to be a mass migration by any means, just that simpleX is a bit better if you are super hardcore about your privacy.
Idk, but I have the same. Scrolling through the tracking methods the only ones with high uniqueness were hash of canvas fingerprint and hash of webGL for me. According to it I still have strong protection Firefox + ublock on mobile though