I think that to hang in something that costs money one needs to have a decent incentive.
One incentive is the fun of flying.
Another one is "required currency".
The rather strange JAA rule that no hours need be flown in the first of the two years is claimed to be responsible for a lot of people giving up. They get their PPL, have little money left, and once they find out they don't need to fly for 23 months, they decide to "take a bit of time off". After a year has gone by, they have lost interest.
Nothing wrong with that - it's their money - but it is a shame for all involved. The individuals lost maybe £10k and a year's hassle in getting the PPL, but the whole PPL scene suffers because nearly everybody leaves nearly right away, leaving more or less just the same old crowd hanging in there. The training business (which de facto owns the primary "scene" at most GA airfields) doesn't exactly discourage this though, by not wanting ex customers around.