They aren't preferred targets so much as they are the cheapest targets.

These scam ads are trying to play the numbers game that email spammers do. So they just bid on everyone at the minimum bid. For people with fleshed out ad-profiles, the big advertisers that pay decent money will buy those slots. The auctions almost never fall through.

For people with no profile, no one bids, and the auction falls through to the scammer who will pay $0.00001 for their ad to load.

So ironically, the (second?) best way to remove scammy ads from google is to keep loading ads from google.