New information:
The alleged victim, @83_5BTC, revealed that after transferring 139 BTC to a new cold wallet, the funds were immediately swept to another wallet by the attackers. The transaction split the sum, sending 55.77 BTC to the hackers’ wallet, while the rest, a staggering 83.65 BTC, was paid as a transaction fee. This incident surpasses the previous high-fee record of 19.8 BTC.
Mononaut, the anonymous operator behind the mempool.space bitcoin explorer, weighed in on the incident. He suggested that “the most likely explanation is that the wallet was generated from bad entropy.” In layman’s terms, this means the wallet’s security was compromised due to weak randomization in its creation process. Mononaut’s insight provides a crucial understanding of the technical flaw that may have led to this unfortunate event.
source So apparently, the 83.5 BTC transaction fee was a programming error (albeit a part of a malware that swept the person's wallet, so I don't think anyone will necessarily feel bad for the hacker).
It makes me wonder how can people screw up their code this badly to spend a large amount of bitcoin on fees, though.
It could be that case or maybe the hackers was in a hurry to get it confirmed, and so he doesn't care about how much he will be paying for the fees, it's a huge hack for him and so he needed to clear this one out very fast and get that bitcoin in his own wallet that he has total control.
As for the individual that has been hack, yeah, he created his own mnemonic phrase or at least add some (that's one I understand it), unfortunately it was not strong enough as the hackers was able to break it and steal everything from him.