The same thing was stated by Statista which noted the number of unique visitors (UV) Tumblr. In January, UV Tumblr was recorded at 437 million, down considerably compared to UV in July 2018 which was recorded at 642 million, as quoted by The Verge, Friday (03/15/2019).
As reported earlier, the official Tumblr content is pornographic on December 17, 2018. A few days before, Tumblr had begun to mark content that violated the new rules.
Using algorithms, Tumblr began to mark content that was considered to violate the new rules. It is content that expresses sexual content and nudism explicitly, but with a number of exceptions such as nursing mothers and classic nude statues.
Since it was founded in 2007, Tumblr is indeed turning a blind eye to the spread of adult content on its platform. But since being owned by Verizon's Oath division, they have begun to aggressively delete these content.