In San Diego there was a fatal crash between a PSA jet airliner, (might have been a DC-9< not sure)
727 versus a 172. The PSA flight number was 182.

I think it's mainly the cost of training and flying expenses. Renting training planes in CA cost $100+/hr wet plus $40/hr for instructor, so total for basic training is $140/hr or more. If you need 70 hrs average for completion of Private license, that's $10,000. If you are an average 40 yr old with family and kids and mortgage, $10K is a very big chunk of money. And after the basic training, if you want to buy a plane, LSAs run around $100K and maintenance by A&P runs $80/hr. With fuel costs at $5-6/gal for avgas, any short flight runs ~$40/hr so a 1.5 hr jaunt to and from is well over $100 cash. Only folks with sufficient money can afford to fly and the average guy can't, so the new pilot's are fewer.
I'm something of an oddity but I honestly think the idea of everyone who wants to be able to fly, being able to do so is not perhaps the best approach. We all know a lot of mediocre pilots and while I too know the sting of the expense of learning to fly in this day and age, I think we have to balance the need to increase our numbers (if for nothing more than political capital) with the need to keep the safety record moving in the right direction. I'll probably get flamed for saying this, but that's how I feel about the subject.