ShinyHunters has a vested financial stake in not leaking the customer data. If they did, nobody would ever pay a ransom to them again. I trust ShinyHunters to look out for themselves continuing to get paid.
Sure. Do you trust every member of ShinyHunters to remain a member of ShinyHunters in good standing, and to resist the temptation to exfiltrate the data in the process of exiting ShinyHunters?
I would expect ShinyHunters to understand that traitors pose an existential threat to the group and to take measures to prevent a lone wolf from selling them out easily. That they have existed for 7 years already indicates they are probably not so amateur as to allow any individual member to walk off with data that would compromise their operation.
No, it actually doesn't, which is the problem. The market has shown that there are no financial consequences to any company that gets hacked. Instructure could have just as well not paid the ransom, as many companies don't, and continued to be fine. Even if they do pay the ransom, it is likely that it is less than it would have costed them to engineer secure systems, so even if you take paying ransoms as necessary market incentives still steer you to ignoring security.
Theoretically, if it happened before and the ransom wasn’t paid, there’s both an incentive by the service to improve their security practices and a disincentive on the hackers to target that business.