Why should everyone be forced to give away their phone number?
Why should everyone be forced to use the same app including it's limitations?
Why should everyone be forced to make a contract with the same vendor?
It could well be that it's not a requirement, because people don't think about it or take it as given.
Imagine Email or phones would work the same way Signal works (with respect to the above concepts).
Is non profit a requirement for most messaging app users?