Most ransomware groups just want the money; they don't particularly want to inflict damage on their target. If their demand falls within policy limits, then they will very likely get payed. If their demand exceeds policy limits, then the target needs to make a much more active decision about weather or not to pay. Combined with the fact that exceeding the insurance limit likely puts you into a realm where you are asking for a some large enough to be a significant challenge (otherwise they wouldn't have bothered with insurance), and you are now reducing the likelyhood of getting a payout.

I would expect the net result of this would be that groups raise their demands to match what (they think) the policy limit is.