Exactly. It is for 'everyone'. Including criminals, gangsters, money launderers like SBF and those using Signal's encrypted cryptocurrency wallet (MobileCoin), terrorists and illegal drug traffickers.
If Microsoft, Google, and Amazon wanted to, they could just refuse service to Signal due to this and cut them off their services for facilitating that since they are centrally using their services.
If they can do it to Parler, they can also do it to Signal as well. Easy.