Only problem is, the average user gets hooked to the shiny UI, not to the invisible backend.
When Microsoft bought Skype, they switched from a secure P2P network to a server-centered network easy to mitm... and the majority of users said nothing. Later on, they switched a few UI elements, and suddenly there was a user uproar.
If Beeper gains any traction, a shiny privative UI is their out to monetize/enshittify the service.