And yet most people, young and old, pick proprietary communication platforms that enable exactly that with more steps. Discord, etc.
If your options are social isolation or giving up your privacy, the choice is rather obvious for most people. And yes, not using the apps other people use does mean social isolation. Sure, your closest friends will contact you through other ways, but less frequently than they'd do if you were in the contact list of the app they use every day.
Discord is by far the most usable, accessible group chat I've seen.
People use Snapchat routinely for privacy not merely because of the hallmark feature wherein it (only supposedly, of course, as this is so easily defeated) helps you control images you send: it is so that they don't have to give their phone number to the guy they just met at the bar and are unsure they can trust, as giving out their phone number means people can trivially stalk you as having a phone number is essentially game over for privacy of everything except the content of the messages you are sending.
Using phone numbers means it is also prohibitively difficult / expensive for people to maintain multiple identities, which I will claim most people do these days (as younger generations are actually deeper and deeper into understanding the privacy tradeoff!!), whether to have a "friendsta", a "shitposting account", or to simply isolate circles. The people most in need of privacy thereby can't use Signal as it would publicly tie together all of their normally-separated personas (unless, at least, they have the money to buy and maintain multiple phones... which, of course, almost no one can).
And like... it doesn't even make sense for really serious cases like political protesters and dissidents! Your biggest actually-realistic issue--certainly at the local level (which includes most of the anarchists and extreme leftists I've met)--isn't going to be an international subpoena on Telegram or whatever: it is going to be an undercover cop getting into your online chat channel (maybe by taking a phone off someone who they arrest), who can now tie everyone's identity together--including people who aren't active in person (and so will never be caught by a cop at the venue)--without any serious effort using the phone numbers in the group (which even includes a list of the people who aren't actively posting anymore).
So yeah, sorry, but no: that Signal is requiring phone numbers for people to communicate privately is them building a UX that actively undermines actual privacy in a way even normal non-technical users are smart enough to realize isn't useful for them, and that they not only don't see it but then decide to spend all of their time throwing down against companies like WhatsApp--which use their protocol!!--instead of declaring that battle won and moving on to fight Snapchat and Telegram, isn't just incompetence... it is a travesty.
Let's put it this way: can you ever imagine a college student who decides to make the difficult decision to go into online sex work for a few months (which is a situation which already really sucks, btw; like: don't get me wrong here... society is fucked in every direction on this issue) being able to use Signal? There is a GOOD reason why these people--who absolutely are clinging to the shreds of their privacy way more than I ever have in my entire life to date--are using services like Snapchat and Telegram (or, if they are willing to make the tradeoff on getting some viral or even algorithmic discovery, Twitter, Instagram, and TikTok) and simply DO NOT use Signal.
Which is completely irrelevant because a typical circle of friends, even among techies, will have one such person at most, who will be mostly isolated anyways.
It's worthwhile to consider a balance between convenience, plausible deniability (people don't really want to be that guy in the coffee shop on Tor), and privacy. Privacy platforms nowadays consider privacy above all else because most people heavily into privacy are purists that don't want to sacrifice any privacy in exchange for having more people to talk with. It's one of the reasons I still respect Telegram with all of its shortcomings, because even though it's relatively insecure in comparison to its competitors, it takes convenience into account and as such has more users than most all privacy-centric messengers while still providing end-to-end encryption for the people that desire it (at least in theory, the cryptography's a bit shaky).
Discord is a superior chat mechanism for modern smartphone internet users in the same way that using crutches is a superior walking method for people with a broken leg.