It's actually a big circle jerk that benefits the airlines. Most of the strategies that Ben and his cohorts promote is "gaming" credit card signup bonuses. Basically, sign up for X credit card and get X number of of frequent flyer miles. The airlines sell the miles to the cc companies for much cheaper than a consumer could buy and in return get some revenue and customer loyalty. In the case of co-branded credit cards, there's probably some revenue share going on. The credit card companies then incentivize a new customer by giving X frequent flyer miles after X spend threshold. The CC companies make money by charging retailers a merchant fee for transactions. The bonus miles they give to new customers is often itself cheaper than what they'll earn in transaction fee from retailers, but almost certainly after you take into account the lifetime value of the customer. The customer feels as if they got miles for free or super cheap as they often make purchases they would have made anyway on another card. And of course, bloggers like Ben get paid on affiliate fees for promoting specific credit cards.

I'm not sure they care. They may be accepting these users because the programs are profitable for them in how they increase normal customers spending patterns.

Tightening up the rules or banning these users might be bad PR for them they don't want to deal with.

It's not strictly about being a bad customer of the airlines... You can get free flights by being bad customers of other businesses offering airline miles (like credit cards) or by defrauding taxpayers (the well-known "buy dollar coins from the Mint" scam). This might even be profitable for the airlines. Sometimes.