I don't feel like I "moved to" Tumblr. I ran out of things that seemed like they'd be best expressed as LW posts and stopped being motivated by karma circa I think late 2010/early 2011 and my posting dropped off considerably. It was the end of 2012 when my sister convinced me to get a Tumblr, and I don't even mostly Tumbl about rationality (mostly). Scott has a Tumblr I think explicitly because he can dash off posts without worrying as much about quality, there; Mike has one for very similar social reasons to my own; I don't think most other people I can think of who are big on Rationalist Diaspora Tumblr were ever heavy posters on LW, although I could be missing some who don't have corresponding screen names, or forgetting someone. They're to a substantial extent different people who happened to enter the circle of interest when Tumblr was a reasonably effective way to hang out on a space with rationalists in it, and so they did that, because for whatever reason it was comfier.