“Experts say the biggest reason ransomware targets and/or their insurance providers still pay when they already have reliable backups is that nobody at the victim organization bothered to test in advance how long this data restoration process might take.”
Having backups is not the same as being able to restore them. A few petabytes over the internet can take months. The ransom gets you running in days, so the insurer pays. Every one of those payments funds the next attack.