His reason can be found here:
Wynn wrote in a now-deleted post shortly before the liquidation:
“I do not follow proper risk management, nor do I claim to be a professional; if anything, I claim to be lucky. I’m effectively gambling, and I stand to lose everything. I strongly advise people against what I’m doing.”
Source:
https://cointelegraph.com/news/james-wynn-deactivates-x-accountHe is a lesson to many people that thinks leverage trading is good. If he was using just 1x leverage, he would have been a good trader. I remember some weeks ago that he posted the market will fall but maybe he went on short position but bitcoin increased and got to all time high instead. He has been losing and losing.
I am kind of sorry for him but people should learn from him.
He's the new version of "Inverse Cramer" where investors are going the opposite of what he's saying. In this case, traders are going the opposite of what his position is hence, him losing significant amounts of money these past few weeks.
I'm think that there might be some retail traders out there that made money just by positioning themselves the opposite of what this trader is doing. As for his account being deactivated though, I'm pretty sure many will just forget him in just a few weeks to a month, but he's a perfect lesson to those traders and aspiring traders like you said. Traders, and those aspiring ones should know how risky trading is particularly leverage trading. In his losses, he always go for x40 leverage which is very risky, and we know what happened to him.
TBH, I learned from his losses and since then, I minimize my leverage especially when it comes to altcoins. Usually, I always go for around x10-x15 or even x20, but now, I always go on x5 only, and for Bitcoin, around x20. There might be saying that it's too high, but I know the risks so... yeah.

How on Earth does someone have a nine-digit account and not know anything about risk management?

Correct me, but he's a gambler (based on what he said), and gamblers don't know about risk management. At least that's what I understand.