Wow, this is really interesting. So CS actually knew what risk it was taking, the hypothesis that Archegos had kept its positions private from several lenders is false. They knew what was going on and couldn't ask for more margin, and when they did without a response they couldn't get themselves to just close out the customer's positions.
The problem is actually one of internal incentives, from my reading. If you've ever done business with CS (I was a PB customer), you'll notice there's a bunch of different entities, far more than you'd expect. I suspect when you have a number of committees in charge, actually nobody is in charge.
You also have a sales guy / risk guy issue here. Some person is in charge of the relationship and gets paid for bringing in the business. Another person is supposed to say stop once the risk to CS gets too high. There's a natural tension there and if the ownership over the relationship is vague, there's going to be a lot of meetings and not much decided. I saw this first hand at a firm I was at: risk guy comes in, asks to reduce positions. Trader says meh and then if there's no process the issue just sort of sits there awkwardly, with no resolution. Normally there's no blowup, but sometimes...
Another PB I worked with had a similar issue. A high rolling Gulf guy came in, wanting to do big FX trades on little margin. Risk said no, boss overruled them. Dude blew up, PB lost a lot of capital, boss got fired.