This shows the downside of network-effects so succinctly. It's almost hopeless to think people will realistically move to a technically superior alternative without this privacy hole.
It doesn't help that, last I checked, the good (open) alternatives were all much jankier or missing one or more major features we use. Makes them hard to sell. :-/
It's better to cultivate that flexibility, than to convert people to flock to the next latest one true DM app.
/s
This will be true for a lot of people, and it's a huge annoyance. The only things that break this kind of network affect is a market changer - Discord is a good example here.