Couldn't these companies use a public/private key to encrypt a special message that their apps could receive and verify it's signed by the mothership and then p

Couldn't these companies use a public/private key to encrypt a special message that their apps could receive and verify it's signed by the mothership and then proceed to relay message or send unencrypted traffic? I mean, there are technical ways to make this work in a secure way (maybe not using my example). This discussion seems old and all safeguards are supposed to be in the law (warrants and other legal devices), IN SOME COUNTRIES. And here's the key of this discussion, should FB/WhatsApp and other be above the law? Why is the government being so careful with them and it wouldn't be if this was, say, Verizon withholding phone records in a specific case if there was a warrant?