Back in '06 I was an intern in the tech department of FINTRAC, Canada's agency for stopping money laundering and terrorist financing, so my knowledge is outdated and only specific to one country- but everyone has roughly the same rules and goals with these laws- track large money movements to find money laundering operations and stop money from finding it's way to terror groups. They use the $10,000 rule- banks report your info if you move more than that in or out of your account and border security reports it if you move that much in cash across a border.
Over time though, new tricks are always figured out, and laws updated. In '06, it was casinos ("yeah I won big last night, that's where the money came from"), currency exchanges ("oh yeah, we do a huge amount of business and over charge everyone"), and jewelry stores (buy diamonds in cash, carry them over borders instead of money). So reporting laws were updated.
Now the trick is "I bought a lot of bitcoins in 2009 and finally sold them today, that's where the money came from". If the laws aren't updated, money laundering becomes easy again.
What else do we expect governments to do? Now, are these laws well written and not overreaching? I'm not sure, and that's worth debating.