When I was in Japan in 2011, nearly every girl I talked to had the same favorite singer -- Lady Gaga. I noticed that Japanese pop culture diversifies in time rather than space: something reaches critical mass and then sweeps the entire nation like cherry blossom season, only to be swept away by the next big thing weeks later. Also trending at that time were the anime One Piece and the Disney character Stitch (who had just gotten his own anime which was the canon sequel to Lilo and Stitch and takes place in Okinawa rather than Hawaii). Previous trends are traceable even after they've left Japan: in the late 1980s, Nickelodeon suddenly picked up several shows featuring koalas. What had happened was, a few years earlier, an Australian zoo donated a breeding pair of koalas to a Japanese zoo, and that triggered "koala mania" in Japan with koala-themed anime becoming popular. A similar mania involving hamsters struck in the early 2000s.

Japanese people are individuals, but Japanese society favors the collective, and the person who goes along to get along. Accordingly, people are rewarded for adding their voices to the throngs supporting something that is already popular or favored by the elite, much less so for cultivating individual tastes, which are pushed to the sidelines (think back-alley Akihabara with its tsundere maid cafés and other businesses of peculiar interest).

In the USA we put high value on "being an individual like everyone else". Social media has simply amplified the "like everyone else" bit by making it easy to keep track of what everyone else is doing. Something that's been ongoing in Japan for decades if not centuries. (The koseki can be considered a form of paper-and-ink social media.)