Its not just the amount of kids, but what you do with the kids you get. If all it took was more kids, Reading & Upper Darby would win everything. While Garnet Valley's numbers are growing, they are still the smallest 6A school in the Central League. But they do more with their numbers than most schools, especially Ridley.
I always liked using participation numbers as a barometer for schools that have active and thriving sports programs. For example, GV has approximately 840 boys in the school. For spring sports only, the have a 90 person track program, 100 person lacrosse program, 45 person baseball team and another 40 playing tennis. So about 1/3 of their boys are doing a sport. If you factor in another 100 kids lifting every day for off season football, and the percentage jumps to close to %45 of boys doing something athletic in the spring.
Ridley has about 100 more boys ( about 930), but has about 50 for track, 50 for lacrosse, 40 for baseball and 15 for tennis, or about %17. Toss in another 50 kids lifting and the number jumps to about %22 , or and half the number that GV has. If you add in girls, the nujmbers get progressively worse.
Bottom line-Ridley has less kids doing sports by a large margin compared to the smallest school in its classification. And you cannot win with those numbers. Now, why the kids arent coming out is probably for many of the reasons others have posted. But I do not think its just demographics or economics becuase if that were so, you would not have the Coatesvilles or Harrisburgs of the world.