The only criteria for purging an account seems to be ’several years‘ of inactivity.
Twitter is set to start purging accounts that have been inactive for several years, according to Elon Musk.
In a tweet yesterday, Musk said, „We’re purging accounts that have had no activity at all for several years, so you will probably see follower count drop.“ No further detail was provided as to when the purge will start and what exactly counts as „several“ years of inactivity.
Twitter’s current inactive account policy states that users should log in at least every 30 days to keep their account active. If they don’t, and after a currently undetermined period of time, „accounts may be permanently removed due to prolonged inactivity.