TBF that's not really all they have to do. They also have to use that new application, which means (further) diving their communications stream. And it means an additional onboarding step when they set up a new device.
I understand these aren't huge obstacles, but I am generally reluctant to add additional communication channels for these reasons - they aren't trivialities to everyone.
Email is much easier because of forwarding (or polling, in case an old service doesn’t have forwarding). I’m changing my main email every ten years or so and have few degenerate addresses like apple or yandex accounts which are dead but still attached to few orgs.
Messengers usually don’t have forwarding or a sensible polling interface. It would be nice to have all-in-one app even with limited functionality, since I’m mostly using text and images. Or use one of real full-featured messengers with gateways to others.
I said same things to most of my closer people and in the end they tell me “well they have all our data anyway”.
And all they have to do is just download an application.