I agree about how Tumblr kind of makes a mess of the fandom experience just in general, but I also think, anon, that you might be overestimating the overall popularity of Tiger and Bunny. I'm a big fan but it still seems like a larger-sized niche fandom to me.

There are quite a few really dedicated fans but it's not some kind of big cultural anime watershed fandom or anything. It might become that eventually, if this season doesn't end up a total disaster of >:Fail and if the second season is at all good, but give it time. Niche fandoms take a while to grow and will never garner the support of other bigger anime fandoms, like how big FMA fandom used to be in its heyday.