The reason Keychat is so adamant about using Bitcoin ecash as stamps is that free services are unsustainable.
A blog post by Signal from last year discusses the costs and losses involved in running Signal.
"We estimate that by 2025, Signal will require approximately $50 million dollars a year to operate.”


Signal Messenger
Privacy is Priceless, but Signal is Expensive
Signal is the world’s most widely used truly private messaging app, and our cryptographic technologies provide extra layers of privacy beyond the...