I think I have a reason why those people love Tumblr more, and ironically it was brought up in a LJ community. XD

I tend to agree one of the main reasons lots of people use Tumblr is the instant gratification of someone else liking/reblogging your post. Sure, there are tons of pictures and gifs but it's highly impersonal website, which I partially think is because all Tumblr posts can't be friends locked. I guess if I had to put this in LJ terms, it's like one of those capslock communities for fandoms, except you're not limited to just one fandom because you can talk about all your fandoms.

I have a Tumblr but I only use mine to share something I find funny/interesting/etc. I want to share with others, no matter who follows me. That's why my Tumblr can have an informative news article for one post, then the one after it shows a funny video, then the next is some gif for how I'm feeling at the moment. But at best Tumblr is just a Facebook/journal thing that really needs to fix its reply feature and put a limit on how many gifs can be put in one post. Two or three gifs might be cute but to hell with the people who post fifty or more in one post.