I vaguely recall it being possible at one point for an attacker to get into someone's voice mail by spoofing the target's caller ID and calling their carrier's voice mail access number. Was it something trivial to pull off like that? (Not to trivialize how violating that would be.)
Another was some networks had a voicemail number you could dial into from abroad and then enter the phone number and pin of the voicemail box you wanted to access. Before this scandal nobody has ever changed that pin, or known about it, in the entire history of british telephony.
You could also call something like 07700007123 and then it would ask you to type your phone number and remote access PIN. Almost nobody knew that you could do that, and so almost nobody changed their remote access PIN from the default 1111 or 1234 or 0000.
One 150-year-old newspaper, News of the World, shut down in 2011 when it came out that they'd hacked the voicemail of a murder victim and, prior to that, several British military personnel who were killed in action. It wasn't publicized as to whether this was done via spoofing or via access to law enforcement tools.
because they listened to the voicemail the family of the victim thought the victim may have been alive.
no jail time means none of the people doing this will stop.
no meaningful financial penalties mean no businesses will stop, and no jail time for executives that approved it means they'll remain ok with it.