Why do they lose that ability?
Discussion
I will speculate now because I suspect anyone knowing the answer for a fact is never coming back here. So here it goes. It's a mixture of indoctrination aka schooling, bad nutrition, distractions, retarded parenting as a consequence of their schooling, peer pressure and so on.
0-7y is a very special time in a child's life for many reasons. It's like a trial period and a blueprint for the rest of their life. Tbf, a fringe minority get to keep such abilities later on. Again, I'm speculating. Hope it helps in your quest.