This is a v. interesting debate!
I think a lot of it comes down to people knowing what they want to do with the license once they get it.
For many flying from A to B wth no particular reason to do it apart from the fun of flying wears thin very quickly.
I passed my PPL in November and i've gone straight into Aerobatics. For me, the whole point of learning to fly was to 'do' aeros and i've been lucky to find an instructor and aeroplane (thanks for the steer, Stik!) that keeps it affordable (just) and definately keeps it fun. It's the best sport i've ever done in my life and I find that it really pushes me and develops my confidence in an aircraft.
I'd suggest that every club offers a package to newly qualified ppl's. You could purchase an aerobatics package, an air racing package, touring package etc. All areas of flying could be sold as a one off product developing increased revenues for clubs as well as providing that incentive to continue past the first year.
Many clubs do offer aerobatic/racing/touring/ type courses but in the same way that many of us have a carreer development plan why don't clubs give it's students a flying development plan. Set it out for the studes at the beginning.
Better still why can't we develop the PPL into these packages. I knew I wanted to do Aeros from the start so why couldn't my PPL have included a short course in aeros? Likewise for the pilot who wants to go abroad or take part in precision air racing. Let them do a PPL that centres on these areas of flying.
A bit of eduaction into the endless benefits of having a PPL at the beginning of the PPL course would pay handsomely in the long run.