[…] the company used to charge advertisers for any kind of ad engagement, including favorites and retweets. Over the past two quarters, Twitter has transitioned to a new pricing model, only charging advertisers for clicks that they want — like an app install or a website visit.
Because of that, Twitter is charging advertisers for fewer clicks and bringing in less money. The hope long term is that advertisers will find these ads to be more valuable (they’re no longer paying for “engagement” metrics) and spend more money with the company. That obviously hasn’t happened as quickly as Twitter had hoped.
Twitter engagement metrics for advertisers were a problem. People tend to view their streams as personally curated channels and can react negatively when they receive Twitter ads in their feed. This is especially true when they feel the Twitter ad is not relevant to them. And compounded when ad frequencies increase as advertisers get more aggressive with their campaigns. At times the advertiser was paying for engagement that contained negative sentiment toward the advertiser.
This change is meant to combat these issues and align the advertisers interests with those of Twitter.