Reddit makes it much easier for any web traffic to follow through to ads. The issue is that Reddit doesn’t have a mature ad network infrastructure team to care about filtering traffic to better standards.
Given that only 50% are jokingly fraudulent, I’d say they’ve already done an OK job and aren’t booking an order of magnitude more of the web’s typical random traffic.
Ad buyers will pay half as much for double the traffic when half of the traffic is bots.
Every ad links to alb.reddit.com . Every post links to *.reddit.com .
E.g. if you have a bot to click on ads to make you money, you'll be less likely to be detected if they also click other ads / have other background advertising data. Similar to how spam review accounts will also leave reviews on entirely unrelated products, both to appear more real at a glance (not just one "5 star buy now" review), and to throw off detection of "this account is obviously paid by this account".