But in the same respect, the fact that real human social activity is much more random is a reason why this should be easier. Bots are inherently pattern based, and while there are bots that could work to maintain fake interactions in order to pass a wide-sweep analysis of low-socializing accounts with a high ad response rate, it would do quite a bit to take a first attack on some of the more obvious bots, which are the ones that many of the people who had these problems noticed.
Now of course I'm simplifying this to a nearly absurd degree, but I do think there are reasons for Facebook to want to ignore these issues and that even a minimal step up in bot-prevention could go a long way when it comes to their advertisers.