1) Because Japan is a great direct competitor to the US, as far as nations with top resources. Japan has had far worse results than the US on the track, despite much more interest and participation, per capita. There is nothing misguided about it, when your first question is “out of how many?”. The US has 40 million who identify as joggers or participated in jogging. Approx 1/10. Japan 1/5 of the population is runners. This is just one industrialized nation as an example of how the US pool is not as large as you think.
2) I brought up the 800 in response to the original poster who YOU responded to. The sprints and throws just show that USATF has had wild success. Just because they have not swept the distance events doesn’t mean the US isn’t BY FAR the most successful track and field nation, and it isn’t close.
3) I don’t need to reiterate RunningArt’s comment that Galen Rupp and Evan Jager won medals. That speaks for itself. The last 10-15 years, US born distance runners (yes, 3k-10k) have encompassed the 2-4th best nation in the world, based on results. Considering the talent pool, it is the best non African nation, and as I stated, that is BECAUSE of the large resources.
4) You don’t get to conveniently ignore women in discussions like this. Their success matters and is part of the USATF model. In fact, I would argue that their proportionally higher success is a strength of the developmental program, and it should be lauded.
5) The US has had as many medals as expected, and perhaps more when you count Centrowitz’s gold, Manzano’s silver (came through the American System).
You don’t get to conveniently ignore the 800/1500 and act like the US has had a poor distance running scene. Do you expect one nation to dominate every event, at every level? That is statistically unlikely, and the as I stated the US population participation is NOT high enough to expect this. They are competing against the rest of the WORLD.