They address this directly in the article. The previous horizontal crop was not an arbitrary design decision, it was put in place to improve the browsing of twe

They address this directly in the article. The previous horizontal crop was not an arbitrary design decision, it was put in place to improve the browsing of tweets by fitting more of them into the viewport. Their intent was to improve the user experience. The ML-powered auto-crop was the engineering solution for how to deliver the best version of that. They don’t say it in this article but I suspect the need to fit more tweets into the viewport was obviated by smart phone UI. The screen is tall and it is super easy to scroll quickly with the flick gesture. No need for short images anymore.