Part of the problem for this also lies in the fact that most top players are built into "cookie-cutter LI" builds for U21, so it's hard to then do a complete 180 and make them well-rounded, "ingenious" builds.
For such a build, you obviously need good starting stats in almost every skill and high (9-10) potential, a rare combination in itself. PFs like Ceska's are especially hard; there's probably no more than 1-2 18yo players per season with 10+ potential, adequate height (6'8" or taller), good inside skills,
and good secondaries (esp. OD/PA/JR).
Then, it would really take a high-level manager training such a rookie from his 18yo season with U21 as no more than a distant afterthought, which in a large, highly competitive nation like the U.S., would require a tanking manager who is willing to drop down 2-3 leagues to play 18yos in league games. You don't find too many managers who are willing to sacrifice that much and watch their team get pummeled for 2-3 seasons before their trainees are ready to compete. It's much better for a U.S. manager who wants to help the NT to buy a promising 22yo who's just come off of his U21 appearance and who has the skills to play at a high level while being rounded off for NT contention. In a smaller nation like Ceska or Japan, it's easier to train young players to the exact build you want, without having to completely screw your club's chances over.
Then there's the psychological element. When your player gets to be 23-24 and is already a viable, above-average starter regardless of level, pops start to slow down and you have new trainees to take his place, and further out-of-position training will only hurt your team's success, a lot of managers will call it quits and decide making a player who may or may not even make the NT, depending on the tactics used by that particular manager or random GS factors or the strength of the competition. I can think of several managers who have bought excellent trainees and promised to train them to NT stardom, only to fall by the wayside when they realized how long and bleak the road to that destination can be. I'd be lying if I didn't say I've done the same myself.
Obviously there are some U.S. managers who will make these long-term sacrifices (daryk with Ronald Colorado
(27250578), and as a community we're making plenty of effort to get the job done (scouting, mentoring, training players ourselves, etc.). I think we would be the first to admit that we would like to do more in this area, but at the same time, I can understand why jfarb, Coco, and yeppers would be upset by you calling us out for not doing enough with little knowledge of the actual situation. It comes across as dismissive of all the effort our top managers and coaches have invested in the NT pipeline, and it comes across as if you're being slightly arrogant by backhandedly telling us that your player is what our NT players/prospects
should be like.