might be because the US probably doesn't express any interest in them from when they're kids
and yeah when I saw the name Weah I was like

Good to see there's an african legends son on the come up out here
It gets tricky when it comes to kids and deciding to play in the country where they live or where their families are from. Been this way forever and not just in this country.
I do think there is a discord between the inner city kids/poor communities/kids of color and the development of the USA soccer team, but I think some of the MLS academies are starting to look into these areas for talent.
The Seattle Sounders signed a deal with Merced Youth Soccer Academy based out of Merced, California. Merced is a small town agricultural town with a majority Latino population in 2010. 2 of the kids from Merced have moved up to Seattle and are now training with the Sounders youth teams. Alfonso Ocampo-Chavez is on one of the USA youth squads and scoring goals in worldwide tournaments.
Notice the trend in this picture?
The Sounders also brought in a kid from Las Vegas at the age of 13 to their academy. He won the Golden Boot at the Youdan tournament in Sheffield, England with 5 goals and 2 assists in 5 games while the Sounders won the tournament in their age group. Now at the age of 16 he's signed a professional contract with the team.
I think over the course of the next 5-10 years the demographic of the USA team and the kids playing this sport is going to change.