Probably because it requires actual effort so why not purge everything to give the illusion you’re actually doing something?
As someone who has copped out of doing work in order to do as little as possible, I think that’s an accurate guess. I mean its like how instead of actually cleaning and putting stuff away, I just shove it in my closet and hope nobody looks. And now I have a perpetually filthy closet that’s too much work to clean. But at least for a while the rest of my room LOOKED clean... at least until it got dirty again and now I have no space in my closet so I pile things up in corners and on top of my bed, while at least having some stuff organized under my bed.
Yeah Tumblr’s doing the online equivalent of that. Incidentally, that’s also how I hid whatever smut I got ahold of. So yeah, that sounds like what Tumblr is doing.