Count thats a easy question. I think the reason is most Ba Gua Zhang practitioners never learn the Metaphysical part of the 8 mother palm circle walking method.

Many can't even walk the circle maintaining their fundamentals of Ba Gua theory of movement and body integration, but you see them trying to learn all these pretty looking Ba Gua Zhang forms. And when it comes to utilizing Ba Gua Zhang in a real fighting situation they can't apply nothing from their Ba Gua Zhang training.

The reason why is because they have not develop the real internal energy or fa jing from their 8 mother palm practice. So even if they was able to apply the principles of change it will do them no good if they don't have any real Chi or fa Jing power develop.

The way I was taught the 8 mother palms circle walking method is practice to increased one's Chi flow, develop good structural alignment that will lead to a dramatic improvement in one's body mechanics and Fa jing power from the moving postures. The next level is more metaphysical method and theorys of playing with the Chi (energy) one has develop, transporting the Chi methods. When one has this method down then they can move on to learning single palm change and the Gua's of their Ba Gua Zhang system.

But today most Ba Gua Zhang students go right to learning single change of palm, with out first developing their Chi, Body mechanics or Fa Jing power.
Thats the problem I see today with most Ba Gua practitioners. The other problem is many are just learning from fakes with no real Ba Gua Zhang knowledge.