Why PgMP & PfMP no. not growing very fast?

Why the no. is so low for PgMP and PfMP certified professionals around the world.

1. The application process is really very challenging.

2. The exam & re-examination fees are very high for many professionals for the most part of the world

3. No good reference materials available for preparation.

4. A handful of trainers or mentors available for support.

5. The exam has rally very high standard and the passing percentage is very low.