Basically, looking at history of federated messaging protocols (SMS and email), they are permanently frozen in time, and haven’t had security improvements for decades.
Signal team considers this tradeoff unacceptable, as highly targeted individuals rely on Signal to always keep it’s security model up-to-date against the most capable adversaries.
Signal people have already explained why they refuse federation.
Basically, looking at history of federated messaging protocols (SMS and email), they are permanently frozen in time, and haven’t had security improvements for decades.
Signal team considers this tradeoff unacceptable, as highly targeted individuals rely on Signal to always keep it’s security model up-to-date against the most capable adversaries.