My theory is that these bots are tests to eventually have a decent config to gain enough age&karma to have some voting clout. Then the upvotes are used to boost the attackers stories and avoid voting rings.
Any puppet account you recognize is one that has already failed. Just like with websites, time is a major factor in detecting these type of accounts. So if you can get away with posting relatively innocuous content in an automated way for a few years you can build "trust" on these various platforms.