Because that's the viewpoint of a beginner to Japanese as a foreign language/culturekentaku_sama wrote:And why grow out of it, what's wrong with a kanji name? Katakana is kind of boring as a foreign name.
Japanese people see kanji names all the time, and so to them, foreigner's using katakana is much cooler. (Well, they think names written in native English letters is the coolest, but they can't read most of them very well, so katakana is the best)
Beginner's are still conditioned with the exotic-ness of kanji names, and therefore want one for themselves. Us more experienced folk have absorbed the feelings of the Japanese people around us, and are tired of hearing "Yeah, that's okay I guess... but it's hard to read, and I think your katakana name looks a lot cooler" every time we ask a friend about a kanji name we thought up for ourselves.