Maybe it's the American in me, but I have almost no use for a payment mechanism in my messenger, I have too many. Venmo, Cash, Apple's thing, Google Wallet, whatever -- these all provide everything I need when I need to send money to people. Frankly the idea that I suddenly might have to have
another goddamn thing is a bit irritating but I've resigned myself to it.
I think the other thing is that it's just a complete misread of how normal people even think about crypto. Literally every "normie" I know who has interest in cryptocurrency, even if they tow the line and say that "crypto is the future of money" or whatever, treat it entirely as a speculative asset when it comes down to it and that's what their usage of it revolves around. It's a thing they put $5 and that $5 becomes $10 later on and now they have $10. Sending it to other people is literally the last thing they want to do. As far as they're concerned, it's the exact same way the stock market works, only faster. None of them care about deflation or border politics or monetary privacy or whatever; it's practically just a way of flipping a bullshit asset into fiat cash, which is what matters. If they want to give people or their drug dealer money in a way that isn't on the record, they don't pull out their instant messenger and say "Let's use a blockchain to preserve our privacy during this transaction", they "pull cash from an ATM and do it in the bathroom of a bar" or whatever. They arrange this over SMS, probably, or maybe Signal already if you're lucky.
Finally there's people like me, people who neither care that Signal is non-federated and don't care that it uses phone numbers, but who just think the cure is worse than the disease here. I'm not even talking about the politics of money exchange or privacy or anything; I just literally mean cryptocurrency invites fraudsters and scammers and all kinds of bullshit along with it, that ends up causing external harm to people. I don't want Signal to expend resources on this stuff because even if it aligns with their goals on paper or is something their competitors might do, I literally think it's turf they shouldn't be on because fundamentally the people who play that game have other goals in mind.