Really dumb. Just a way to cover their own ass. Of course the hackers won’t actually delete the data. This is just so they can claim it was deleted when everyone knows better.

I'm almost sure they do, for the sole reason that when you get a few M$ to set you for life like this, you'd rather start erasing all kind of proof possible (even if your opsec is really excellent) to slowly start building-up your new life, maintaining evidences anywhere is stupid and those guys are far from stupid for being able to pull stuff like this.

That's not always the case.

If all hackers would do that ransomware attacks would essentially become worthless.

It's not uncommon for companies to pay the ransom. They often have insurance that covers it. It's slightly controversial, because paying them essentially makes ransomware attacks worth doing.