I think the reasoning is that the money is part of the evidence. Just like if someone is accused of shooting someone the police are allowed to take the gun and use it as evidence. If someone is suspected of a crime and money is involved than that money needs to be kept as evidence, so it doesn't disappear.
That makes sense. If some junky with a $500 / day habit is found with $10,000 and no bank account then we can assume that $10,000 is drug money.
But isn't that a slippery slope? Imagine if kim dotcom was in the US. Everything he owned, every asset would have been locked up tighter than a frogs ass underwater. He'd be left with nothing to defend himself.
And shouldn't everyone (even the junky with $10,000 cash) be able to defend themselves? If they're guilty then pay back the money. I just can't figure out how people accept the confiscation of assets
before a trial as OK.