Talk:Episodes, films, and shorts/@comment-5663063-20160427141136/@comment-5837525-20160429135659

Probably because Rainbow Dash wanting to be a Wonderbolt has been a thing since season one, so there's less of a surprise factor. Fluttershy having a brother, on the other hand, is unexpected and sure to have the bigger overall reaction because it's never even been hinted at in previous seasons that she had siblings.