Good idea. This is what the article said about their reason for doing it:

The move comes after Tumblr, now under Verizon's umbrella after the 2016 Yahoo sale, has struggled with identifying and removing child pornography and forced prostitution content from its platform.

The company had a face-off with South Korean authorities regarding its stance on adult content last year but eventually agreed to cooperate with authorities in June, and remove some of the reported content.

The site was also banned for a few days in Indonesia in 2016 and perma-banned in March after failing to comply with an order to remove large swaths of adult content from its platform.

But the ban that hurt the most, and is most likely at the heart of Tumblr's decision to remove all its adult content, came two weeks ago when Apple removed the Tumblr iOS app from the App Store. Apple said the platform failed to detect "child exploitation imagery," hence its decision to drop the app altogether, despite its large following and install count.

So it seems it's both government pressure, as well as pressure from their apps being removed and so on.