These platforms generally allow users to withdraw their funds at the beginning, and it was only after he had deposited a significant sum that they disabled withdrawals. They then demanded (and collected) withdrawal taxes, fees, etc. before moving their platform to a different domain.
My friend is convinced the scammer is also a victim who has "lost" 90k by "loaning" it to him in preparation for the pig butchering event. Unfortunately, he's continuing to speak with her and I'm concerned for his well-being.
It's sick how persistent these scammers are - they will isolate and wear down their victims over time until there's nothing left.