I assume video content is much more expensive

They may also have been victimized by the scandal where Facebook was lying about the engagement that short-form videos generated over other kinds of content, leading several content producers into bankruptcy or near bankruptcy through loss of ad revenue when they pivoted towards it.

https://slate.com/technology/2018/10/facebook-online-video-p...

https://www.ccn.com/facebook-lied-about-video-metrics/