It would be curious to know how many coins the criminals have successfully hidden from law enforcement agencies via mixing and encryption, just so we can know if 453,000 coins is a lot of no.
Also, in general this report shows us the importance of privacy - if governments can seize coins of criminals, they can also just as easily start seizing coins of citizens.
A lot is my guess.
Just for one example there was the Coincheck hack which was $500,000,000 of XEM. The hacker set up his own wee sale site on the dark web and was selling it for a discount, but not a vast one, as well as numerous exchanges which weren't fast enough to stop him.
All of it was sold and nothing's been heard about it since. I'm not sure if any of it's left in crypto. Similarly there's Bitfinex's 170,000 coins, Bitstamp's 20,000 or so. All of them got away with it so far.
I assume the only time they can seize coins is a Ross Ulbricht type of situation when a live and unencrypted computer/wallet is captured considering it's so easy to bury seeds or private keys.