all the thiefs have sold all their stolen bitcoins already so supply is starting to dwindle.
where does your source come from? link please?
most of reasons why they scam, is because they want to be in the game for "free" and hold. Not, just cashing it out all the time, why wouldnt they just ride it out? you cant say the supply will dwinlde only cause of this, you can actually look up where most coins are spent.
If you have the list of all these known persons btc address or did it each one, and locate on the spent then thats a different story.
https://www.blocktrail.com/BTC/block/00000000000000000400a987f91bb1f7d219459829693ab15c3ba02deb2a1287