Why? We just don't, thats why. As a fan of Star Trek for years, I found out relatively recently that there was a large core of Trekkers that hated Wesley Crusher. They absolutely hated everything about him, if you push for a specific reason for this dislike you may be disappointed. I think it was one of those things that push Trekkers into being Trekkies (see number 9) as the dislike of Wesley seems a little irrational and seemingly based upon the fact that he was a bit young. I personally always liked him and Wil Wheatons hilarious turns as himself in The Big Bang Theory have only strengthened my affection for him.