Because people make mistakes, and if you make an accounting mistake in a company listed in one of the largest indices, those mistakes are usually in the order o

Because people make mistakes, and if you make an accounting mistake in a company listed in one of the largest indices, those mistakes are usually in the order of billions. So it definitely makes sense to require multiple accountants to check the books of these companies _for mistakes_. Also, running the simple algorithm is the last step of the job. When somebody gives you their books and transaction data, you need to convert that to a format you can first process, which is 99% of the work. Books, receipts, etc. come in dozens of different formats. Running the algorithm is 1% of the job. E&G is required to check that, if there is a receipt from an external company that gave Wirecard 2 billion, and another receipt of Wirecard sending those 2 billion to a bank in the Philippines, that those are properly noted in the books and everything balances out properly. They are required to assume that Wirecard is working in "Good faith", and this is not a German thing: everything else is just impracticable. Even if you were to throw an infinite amount of money and time at the problem to verify that all transactions actually happened as reported, if all sides of the transaction are in on the scam (the company that gave wirecard 2 billion, wirecard, and the bank that stores them), then there is no way for E&Y to find out. If they are aware of criminal activity, they must report it, and maybe E&Y did not wanted to be aware of that, but who knows, maybe Wirecard was just good at scamming, or E&Y was aware of that and reported it to the German SEC. We do know that a lot of people did report Wirecard to the German SEC over the last 10 years due to suspicions of criminal activity, and the German SEC, which is the only authority that can investigate Wirecard properly, did nothing about that.