If crypto disappears today, ransoms will still be prevalent, but will be much higher as they will be more difficult to pay. It's not a new incentive at all, it just opened up the ease of payment.
Like they might accept a ransomware of $200 instead of nothing from person X because they're hitting up thousands of people with it, whereas if you go through all the effort to physically kidnap someone and leave a ransom note, you're not going to be able to do that thousands of times, probably just a couple at most, so you're going to demand a large ransom payment to make it worth the effort, like $1 million+.
They also didn't say 'unpayable', btw, just more difficult to pay.