If you think the demise of tumblr is about anything other than FOSTA, we must be experiencing different parts of the internet.
FOSTA became law in April 2018.
So please explain to us how FOSTA was responsible for Tumblr's demise.
It was a poor experience lacking in engagement. Using Instagram and Reddit was much more fulfilling in creative and online social/community needs.
Tumblr's numbers were flat lining before they removed porn. I know this because my friend was a Tumblr engineer and would share data from their all hands meetings.