Just a quick thought.
I wonder if all of the the twitter bots are a result of people trying to gain free api access to twitter. Normal rules allow a certain number of requests per minute or or something. However if yo were to have 1,000 accounts, you could perform 1,000x that number of requests and searches per hour.
I bet if twitter looked for accounts that were performing high volumes of API requests, they would find accounts that were most likely linked to bots.
I am not yet sure if it is worth it for twitter to remove these accounts or if they are oddly good for the ecosystem.