Really, the PDGA sells a service, and that service is a tournament series + the residual benefit of points and a rating. If you are not interested in the service they provide, there really is no reason to join. The PDGA would waste it's limited resources trying to get casual disc golfers that don't want to play in tournaments to join. About 30% of the PDGA membership is a revolving-door one time membership, that is folks that join once for one year and are never heard from again. That's not to uncommon in orgs like the PDGA. People will join, play a few events, decide it's not their cup of tea and move on. The assumption made is that those people quit playing, but there is no evidence or tracking of what happens to them. I assume many quit playing, but others just go back to places like Hazelwood and keep on chuckin.'
The PDGA is not unique in this. The general estimation in any sport is that only 5% will get involved in any organized activity. That doesn't mean join the PDGA, that means join a league or show up for a club flight. Only a small percent of that 5% will then go on to join the PDGA. So the "organized" wing of any sport only represents a small fraction of the players, but it is that small fraction that do things. The other 95% just play. In most cases all they contribute is their entry fee, but disc golf is free so they contribute...well, you can do the math.
BUT, those people have to be there. I doubt the County would be allowing RCF to use Unger for yet another disc golf course if the expectation was that 200 or so people in the entire St. Louis area played disc golf. The understanding is that RCF is the tip of the iceburg, and the rest of that iceburg has to be there in order for the sport to move forward. Otherwise, there are not the number needed to justify all the public land we occupy. That's the way it is, and the PDGA really can't alter human behavior just because somebody becomes a Frisbee freak.