Because with knitting, you can be a grandmother and be a knitter. You can be pierced and be a knitter. You can be a man, or in middle school, or German, or Pagan, or Catholic, or a chicken farmer, or a geneticist and still you’re a knitter.
And do you know the best part? You can come to knitting group once a week and you get along with all these people, because you’re a knitter. It is the great equalizer (and although I don’t think it could create world peace, it could come pretty close, unless you post about it on a Ravelry forum).