Are you asking why there are so many people who enjoy anime on VRC or why there are so many people wearing anime avatars? If it is the latter, then I would say it is because there was a Japanese game and several well known anime influenced 3D artists who happened to make a bunch of models that upload very easily into VRC. For ease of convenience people began editing those models and uploading more and more hence why there is an overabundance of anime based models. There of course are models and individuals that stray away from that aesthetic, but if you have 50 avatars to choose from, 40 of which are very well made and happen to be anime based and 10 not so well built meme based avatars, your chances of picking one of the 40 are greater. If you just want to know why there are so many people who enjoy anime in VRC, I would say it is due to the fact that there is an overabundance of anime based avatars.