Bitcoin is not anonymous. Should one be able to link a wallet to a real name (like, for example, phil21), they can then follow each transaction that wallet makes, and where every coin ends up.
Once you know phil21's wallet is empty, those looking to heist anything would look through which wallets the coins ended up in, and start linking identities to those wallets.
If a criminal knows to look, they see the risk no longer matches the reward. If they don't know to look, odds are they weren't involved enough to have followed phil21's coins and wallet back to a street address in the first place.
Sure, the risk isn't zero, like you're implying, but it's dramatically lower.