I don't think it's fair to compare virtual items with real life items. If someone hacks your account and then passes the valuables onto another account this could very well be your casual GP buyer. Imagine if they started targetting people who buy gold - perma ban them and give the items back to the original owners, it'd be a fucking chaos.
On top of that a lot of people will insta sell the bank when they get ahold of an account and the gold passes through a couple of different people. If Jagex starts banning those chains which may even up to 10 accounts in rare occasions the playerbase would drop crazy low.
In real life cops have to get certain warrants and what not to search you if they suspect you stole something, Jagex does not have to do anything - a simple command and they see all the info they want to see.
EDIT: You're comparing a public service which you're paying taxes towards and a privately owned gaming company.