Because Signal is suspiciously toxic and hostile towards any fork. So far Molly managed to stay alive, but I'm sure the Signal company will find a way to kill it the moment it gains traction.
Do not trust a network that won't allow third party clients, that won't regularly publish the source code to their server software and that requires your phone number to sign up (and makes it ridiculously tedious to use virtual numbers).
Better use a different platform:
https://xn--gckvb8fzb.com/an-overview-of-privacy-focused-decentralized-instant-messengers/
