Yes, the sport has been growing in popularity, but just because a sport is popular doesn't mean you play it well. Basketball has been huge in China for a couple decades and they haven't seen much in the way of results.
The top American talent that has received good quality training in dedicated systems for most of their life hasn't had as much time. If you look at our U-17 team, they've looked dominant in recent competition and have the CONCACAF championship later next month. They should be World Cup bound after that.
Our U-20s just won their first ever CONCACAF championship on the back of a weakened squad, and are headed to the World Cup this summer in South Korea where they should put in a good showing. A weak pool means advancing is likely there.
Our last cycle of U-20s made it to the quarterfinals before losing to Serbia, the eventual champions. While many of those players are struggling to find playing time now the quality is there. Carter-Vickers, Zelalem, Hyndman, Rubin, Miazga, are a few examples of the talent on that team.
Pulisic isn't the culmination of a long period of US soccer development; he's the first and best of a group of players that is slowly rising through the ranks. Though many will not pan out, the overall talent pool is getting better.