IMHO, it is Google and Apple that are entirely at fault for allowing the software of their phones to grant such open access, with users unable to deny such access. If an ancient protocol mandates a response to be sent, the response might as well be fake. Also, silent exploits of Whatsapp, iMessage, SMS, etc. have existed for about a decade now, which should have been more than sufficient time to close all the loopholes. The only explanation that remains is that Google and Apple are conspiring with a third party to keep phones insecure.