David,
That the touristic destinations of Wales are nowhere near to CWL, if you live, let's say, around Manchester and want to holiday in West Wales would you consider flying to CWL then hiring a car or whatever?
The chances are you, and the majority, would opt to take your own car with you and then have your own transport during your holiday, but were there flights direct in to a West Wales airport I'm guessing that many would need to think twice before taking the car.
And as for Mid and North Wales, well BHX, LPL etc. are far more convenient for these than CWL is ever likely to be.