Or is it more like the 'chicken-and-egg' scenario?
Or maybe supply and demand?
When someone wants to gain a PPL they will seek out a club/school that meets that requirement and learn.
If/when they decide to do additional training they will (should) do the same thing - club loyalty etc only last if the requirements are met...
No-one, except Mr Benevolent on Benevolence-day, is going to set up a flying school on the off-chance that someone might pop in who wants to do something different...