With the tournament winding down I'll do some ruminating
I could argue American men's tennis overall is in a decent spot. By my count, 17 guys qualified for Roland-Garros. I haven't crunched the numbers, but for at least a few years now it at least feels like there've been 10 or more Americans who've qualified for most of the Grand Slams, which was not the norm a decade+ ago. And they’re not all pushovers. There’s also an upper tier capable of making deep runs in slams, with Fritz, Shelton, Paul, and Tiafoe. Now, I completely agree that that tier really has no shot of winning titles, and each has a glaring hole in his game, if not more than one. But for me, it’s at least better than when I started following the tour a bit and Isner was simultaneously the only American who didn't always have to pull multiple upsets to reach a quarterfinal, but was bound to lose as soon as he played someone who could get his serve back and-or move him. (Yes, I'm young enough that I didn't get to enjoy Agassi and Sampras, so that's subjective.)
As for why none of them really has a shot to win titles, I'm sure there are multiple reasons, but it's always a bit of a mystery to me. Soccer is
the sport in Europe. It's really no shock that those countries are effective and efficient at funneling promising players from families with means into academies, and turning a portion of those kids into pros. So people in the US who care concede that we're at a disadvantage out of the gate. But how, then, have almost all the tennis superstars of the last ~20 years been European? I know there are tennis academies here, so it's not like there's no infrastructure in place.
@Letterkenny is right that tennis still doesn't have much of a foothold in the US sports scene, but Spain is not a large country, so how did they end up with Nadal and Alcaraz? I know there's always chance/luck involved, so that was somewhat rhetorical. But my point is I don't know that it's a numbers game. My best guess is that, because a large percentage of great athletes in the US play multiple sports until college, there's just not the same all-or-nothing commitment from a young age, at least to sports that are considered second-tier here