Because the unfairness was caused by pirate which rendered the lendees incapable who themselves are responsible for the unfairness through lying to  Patrick, making it impossible for Patrick to repay his debt except through his personal assets. Patrick then renders it unfair for depositors by claiming coverage of the deposit and not reimbursing .

If I take a large business loan for expanding the operation and lose my funds because someone steals it, it is not my fault and it hinders my ability to repay. But since I'm operating as myself, I personally owe that money because I promised it. I cannot try to void part of the loan on behalf I lost the funds.

I strictly promised the bank to repay the business loan. I argued I had a good credit score and a stable business which would make me capable of repaying the loan providing a business plan detailing how I'd use the funds. But when the bank tells me those arguments are accepted to grant the loan, no party ever agrees the repayment promise is directly dependent on the arguments I offered to hold true and being sufficient. My business went down the drain because someone stole my funds putting me in serious debt. Yet I still owe the bank the funds because that's the only promise I made them. The arguments I gave were purely to convince them. Can I keep the assets I have left and default on the loan because those specific funds were stolen by the third party because I gave it to that third party?

The bank makes the mistake of believing the arguments to be sufficient to expect me to repay the loan.
I made the mistake of badly choosing who I'd then pay those funds to and gave them to the wrong individual which commits a financial fraud (accepting payment and not delivering anything in return.) I myself made the mistake that hinders the repayment of the loan, causing loss to the bank.

The mistake is far from being common. The depositor blindly believe Patrick can be expected to deliver based on his arguments. They put themselve in the situation, it was a mistake, but it does not cause the loss of the deposit being irrecoverable, just like you didn't cause the loss of the test's costs by accepting your doctor's claims.

The loss is caused to the depositor when Patrick loaned the funds to wrong person who then didn't pay him back, something over which the depositor had no control. Patrick bears the responsibility of making that mistake.

The mere fact that the depositor not making the mistake of giving Patrick the funds he asked for his business would have not enabled Patrick to make that loss does not make them responsible. Consider this: should a person making the mistake of handling over a knife to some shady individual asking for it to cook would place that personal equally responsible for the death of someone when said individual proceeds to kill somebody, because you enabled that murder? Both made the mistake to entrust something they shouldn't have to someone they did not really know, enabling a loss to someone (Financial to yourself in the first case or of someone else's life in the later). Both giving party made a mistake enabling something to happen by entrusting their property to someone else, which is a far different from the mistake of doing the mishandling creating the loss when you had no control of it.

When you accepted your doctor's claim, you enabled the loss by proceeding with the test which would have been impossible otherwise. But you did not cause it, the doctor did by promising you would not pay and then the insurer not paying as he expected, so he paid for the test since he promised you would not pay for it. I could argue you are just as responsible as Patrick's depositor who did not do due diligence in investigating before proceeding. Had you had investigated and called your insurer, you would have known the test was not covered and the doctor would not have to bear the loss.

The first makes a mistake which enables the situation to happen. The person who made the promise the other would incur no financial loss makes the actual mistakes which cause his own loss, regardless if he was mistaken on his external parties on which he base his promises (such as the doctor) or if those parties outright scammed him like for Patrick. The mistake is not a common one.

The only common decision is accepting the contract. Patrick's contract was a bad contract. He made lending mistake which caused him to lose the deposits. The contract in itself (That Patrick would be able to cover deposits and pay X%) did not cause the loss. The depositor should have known better than accept such a poor proposition placing himself in the situation. But ultimately Patrick's mishandling of the funds is the mistake which made the promise he offered impossible to hold and created that loss. Not that both entered the agreement and transaction which enabled the loss. The depositor made a mistake in accepting a bad offer but I currently remain with the conviction it is a different mistake that is not common.

I would have ZERO problem with that if Patrick came forward trying to find a compromise or offering to slowly refund deposits personally or attempted to at least try to renegotiate anything and showing he cannot current repay the debt. In which case I would call it a default on his debt because of inability to repay. But so far he remains silent and has done nothing to resolve the situation or shown his willingness to depart with any wealth to cover his debt. Hence why I believe he should be considered as a scammer until his debt is repaid or renegotiated or that he paid as much as he could possibly pay.