Why were Coldcard hackers so stupid?

I don't understand this hack. Most of the funds moved to a handful of wallets. They are now tainted and require mixing and even then they will never be fully unsuspicious.

If they had just generated a new wallet for each one they drained and moved the funds one-to-one you would never be able to distinguish a hack from someone moving their funds to safety.

Second, the high transaction fees paint a signature too. Just start off slowly, normal or just above normal fees. Drain a few accounts. Get the word out. Then slowly speed up, increase the fees. Exactly what people saving their coins would do.

Might not get as many coins as they have now but they'd all be free to spend and beyond suspicion.

How can they find a pretty sophisticated hack and then execute it so badly? It doesn't make sense to me.