So I must know. Why?
Why do so many artists start posting there and none of it makes it to their art gallery here? A lot of artists I love start posting complete works there and neglect this site that simply has a better gallery and message system. They don't post everything they have despite how complete it is.
I'd move there but I've never encountered a UI system that gave me such a migraine until Tumblr. From how impossible it is to find something to how many clicks, wait times, loading, reclicking I have to do to find the top message of a list of comments or even get to someone's page.
Then there's the reblogs. There's only so much I can take from that until someone reblogs their own blogs (morning/night reblog) and that just pushes me over. It could easily be fixed if everyone tagged their stuff properly but no one does. It could EASILY be fixed if people don't reblog their own stuff because there's a feed that I can just scroll back further for.
Just imagine DeviantArt if all you had was Deviation Uploads. And it was flooded with every message everyone has ever made (including people you don't watch), every edit they made, and every time someone favs something I've already seen a dozen times. It becomes a pile of hundreds of duplicates that you can't look through out of order.
That is Tumblr.