Indeed, as the other comment stated, it’s the reliance on phone numbers.
Governments can intercept and block registration SMS and put you straight on the watchlist for even trying
Every single cell provider in the world can make phone calls from your number, nevermind sms, and so does everyone who has influence over them, be it law enforcement, someone with money or inside connections to bribe some corrupt employee, or just a kid with a gsm sniffer, or even just a sharp tongue and gall to just call them and say “Hey my name is Bob Marley, unfortunately I’ve lost my phone, could you send me a new one with the same number”. Yes, they won’t be able to read your messages, but they can register a new account to your number and scam your friends by pretending to be you.
Privacy nightmare, phone numbers carry a lot of private data with them which is very easily doxx-able. I don’t want to share all that just to chat with someone, especially when supposedly talking about something I wouldn’t want someone else to be prying upon. IE if I’m planning a crime I don’t want my potential accomplices to know my full legal name and DOB, which they’d be able to get for just a dollar if they knew my number.
How do you even deal with spam? Admittedly I’ve never used Signal, because of point 1 where government blocked and put me on the watchlist, but in a similarly phone-tied telegram, when my p/n got leaked I got dozens of spam messages every day from random accounts, and had to basically abandon it because there’s no easy way to change the identity
Why?
Indeed, as the other comment stated, it’s the reliance on phone numbers.
Biggest criticism of signal is requiring a phone number imo