Because 0-days are accessible to anyone with money. And Ernst and Young would have a ton of money, and plenty of opportunities where clients would come to them

Because 0-days are accessible to anyone with money. And Ernst and Young would have a ton of money, and plenty of opportunities where clients would come to them and hire them privately about issues like this. Coming up with 0-days is moderately hard with your own cracking team. Buying them is an easy thing to do. Ultimately, that's what 0-days are for in the wider market. You find one and sell it.