It’s not about “smart” as much as perfect execution. Bitcoin’s design is very brittle, so he had to do everything perfectly every time but they only needed a single opening. People try various things to split up wallets but those are complicated for a criminal who doesn’t have many people they trust and targeted attacks by nation-state level adversaries are extremely hard to stop (e.g. for an operation of this level, burning a few million on a zero day isn’t a very big chunk of the budget).
Bitcoin is designed to make it easy for everyone to know you did that. It’d be bad if you had to convince prosecutors that you really lost it and much, much worse if you had to convince your fellow mobsters.
You keep a little bit to give to them, so its not worth it for them to do any crime to you.
Like keep 1B available and store away the other 15, or even give them 10 and keep 5 like they when mobsters have 10 billion they have not much incentive to risk killing/torturing you for potentially 5 billion more.
Same for government, you have negotiaton playground.
