It's a combination of the low-hanging fruit being picked, insufficient investment in novel approaches and not enough geniuses.

but the lesson there is to not spend half a million dollars on your child.

If genius is a limiting factor, and genius is often under utilized, then spending half a million on increasing the odds of full utilization of a genius may be a good investment. If you can arrange for that genius to be your own child, you would be best situated to spend that half million for maximal effect.