Indeed, they have cash from drug cartels, Iran, North Korea but they are focusing on bitcoin. Last year, charges against HSBC were dropped after the UK finance minister warned of a 'global financial disaster' if banks were prosecuted for laundering. https://www.theguardian.com/business/2016/jul/11/hsbc-us-money-laundering-george-osborne-report

Agreed, they probably want to legalize bitcoin so that they can try and tax it. If they find that they can't control it, they'll probably outlaw bitcoin like they did with online sports betting.