I am not sure it is even a question of competency. I think it is a question of motivation. It is the same reason why Twitter doesn't crack down on their bots. Both sites have an inherit interest in appearing popular. Having 50k upvotes or 50m followers looks more impressive than 25k and 25m. It is possible that those companies feel the value of those increased numbers is greater than the potential damage bots do to the community. HN doesn't have the same motivation since HN is more of a vanity project with a bigger focus on the good of the community.