The key detail. If Sonys not willing to pay these 6000 files are not important.
There is no doubt the hackers would take sonys money and then sell the data anyway. You will lose badly by paying them. You have to consider the breach as a total loss if you are Sony, paying up ransomware is foolish decision.
The target for these hacks is always for the company to pay, so companies not paying is a very good play.
And to make things worse, this would just signal to other hacker groups that hacking Sony is very profitable, since they apparently are happy to pay. So they would just increase the target on their back. No upside.
The business pays to unencrypt the files and achieve business as usual operations.
The business doesn't need to trust the attackers not to further share data to get their upside, though I'm sure that helps.
The ransomware groups hit lots of companies. Their reputation for holding up their side of the bargain is how they get paid. So they tend to keep their side of the deal.
The money is better spent improving security. Them spending money with hackers won't stop GDPR from ripping them new asshole either.
Wrong. The "return" is pointing a bigger target on your back because now future attackers know it is worth it to attack you.
As for the backups, the groups running ransomware are very aware of the importance of backups. Therefore they have developed best practices targeting the backup systems in a variety of ways. If the backups are online, delete them. If the backups are offline, compromise the backup server so it stops taking backups, leave that for a while, then do your attack. (You'd be shocked at how many companies don't test backups regularly...) If whole computers are backed up, insert a malware timebomb - as soon as the computer realizes the date, it destroys itself. When it is restored from backup, the backup also destroys itself.
Most companies pay too little attention to backups. And therefore highly motivated attackers regularly succeed in attacking them.