This is really the crux of the problem. ~$3M of servers per year is more than enough to start purchasing hardware, I wish there were easier ways for people like me to participate and help Signal on the cheap.
As someone who participated in the builds they complain about being expensive (and ignoring their , I don't think it's a function of centralization or "troubling" as much as it is practical. Meta, Google, etc all have many billions they could be saving if they could figure out how to make it cheaper too.