And, you don't have be a licensed insurer to display a comparison widget and get paid for conversions...you can drive your margins higher if you have the license, but it's not needed.
In the case of their auto insurance quoting part of the business, they were doing something far more sophisticated than just generating leads for credit cards and mortgages. They were actually a licensed agent and generating commissions from quoting and issuing policies. Auto instance is highly regulated and they need to be licensed to do what they were doing.
Three things at play here I see:
1. You are creating new market pressure on the companies that pay you. If companies offering these products stop paying you, then no one pays you.
2. The level of sophistication needed to operate a full quoting service is higher than one would imagine in insurance and I wouldn't be surprised with other financial products.
3. Just sell ads. It's relatively simple, unregulated (relative to financial products) and works in cooperation with (not against) the hand that feeds you.
Since Google is able to ensure it's the only ad in the SERPS with pictures, and it sits in the top spot, well...
I suspect the hard part is something other than making money on it. Maybe legal, anti-trust or other concerns?