According to research from Twopcharts, 44% of the 974 million existing Twitter accounts have never sent a tweet. 30% of existing Twitter accounts have sent 1-10 tweets. Only 13% have written at least 100 tweets.
Twitter does not consider account holders who have never tweeted to be 'inactive'. Its definition of an active account holder is someone who logs into their account at least once a month.
The more engaged a social media user is, the more valuable they become. Activity generates advertising revenue for Twitter. Similarly it is easier to retain users who are active rather than passive users.
More on this story from Wall Street Journal.