It's not that they're not interested in user freedom and respect. They just have different ideas about what's important. If Signal federates, that will bring to the table all sorts of 3rd party clients who will have say in how Signal does things, yet no duty to comply with the Signal's spec sheet and deploy timely protocol updates and features. Any clients not keeping up are damaging the brand, as was in the case of Matrix clients' poor support for E2EE. Then there's the aspect that the larger the organization managing the spec becomes, the easier it is to infiltrate and clog with bikeshedding.

Signal's strength is its security agility and thoughtful feature design, not federation and availability.