InAfrica - You're not the first person to propose the theory - the bad players will stop playing and then when there are only good players left 75% of them will be relatively bad to the others and they will stop playing and so on until there is only one player left.
What I think actually happens is that after an initial period of heavy betting, while some fish call it a day others continue to play although less frequently. Perhaps having been inspired by a TV show or advert or a huge prize pool. The marketing will not just be about new players but recycling old ones as well.