Earlier quoted context omitted.
If I'm not mistaken, signal is specifically hosted on AWS to so that governments can't just blacklist their IPs without blacklisting all of AWS. So moving to bare metal isn't really an option.
Governments can easily block AWS as well and they have. Even simpler, they just go for the kill-switch and kill internet.
They can, but the collateral damage of doing that is high, which is a deterrent. The only regimes where that's realistically an option are ones where they've consciously developed an independent tech ecosystem (e.g. China) or where their power is so secure they couldn't care less about the damage.