They didn't want it in court because it would have made a documented legal precedent around liability.

"One former partner called the settlement hugely significant because it shatters the distance that McKinsey — which argues that it only makes recommendations — puts between its advice and its clients’ actions. For decades, the firm has avoided legal liability for high-profile failures of some clients, including the energy company Enron and Swissair, Switzerland’s defunct national airline."

https://www.nytimes.com/2021/02/03/business/mckinsey-opioids...

1. I think that’s making a guess into their intentions which we’re not qualified to do

2. Even if we take #1 for granted, the $500MM figure is still based on something. The counter-party could’ve settled for $100MM or insisted on $1B but they reached that number for a reason.