It’s not that AJ is in anyway an unpopular character. Her appeal is wider than most think. Being the most preferred Pony in places like Japan and some part of the European fandoms. She has a large share of devoted fans, and is in general well liked. principled, responsible, honest, and has great dynamics with other characters. Just that the odds were stacked against her by several more “superior” characters among her. It’s pretty difficult for earth ponies to gain popularity in general in the fandom. Earth Ponies just seem shafted compared to the others.