3 things costing us are:
1. As you mentioned too many people support other teams. In my Grade at school of over 100 people 5-10 supported Penrith.
2. 8500 Juniors and about 2000-3000 officials get free passes to all games. Potential members lost there.
3. Lack of success for a number of years now. Not making the finals since 2004 hasn't really pushed those 'fringe' fans to commit to a full year.
The Junior passes are not entirely true.
I'm involved with one of the bigger Jnr Clubs in the Penrith Junior League, and I can assure you that not all the kids get the junior passes.
I know my 2 boys last year, both were in the U/6's, did not get any free junior passes for the Panthers home matches.
I went to St Doms in the early 90's and there was a healthy portion of Panther fans in my year, but as we both pointed out there was also a x-section of other club fans.
Penrith has been in the NRL for long enough now and the city has grown quite large over the last 30 years to warrant more than 4000 members.
I'm just annoyed by it, as I don't want the AFL getting any sort of leg up out here, while I don't support the Panthers myself, I do like seeing them getting big crowds and strong support.