The Bad ... Sort Of
They could drop that far if their defense falters at all. When the USA players are tired, they can fall off tackles. When they commit silly penalties, they can give up tries. And seeing as they can't score them, giving up tries is a problem.
(As we noted in an earlier article, three tries is the magic number. Teams that score two tries lose the majority of their games. Teams that score three tries win the majority of their games. The USA is bucking that trend. Overall this season the USA has scored 0 tries twice (0-2, obviously); 1 try four times (1-3, which is very good), 2 tries nine times (6-3, which is incredible ... the losses were to Australia twice and to Fiji once), 3 tries four times (4-0, which is also incredible), and 4 or more ties five times (all wins).
Think of this way. Here are the winning percentages for teams that score four or more tries, three tries exactly, two tries exactly, and one try exactly not including the USA, and then the USA's numbers:

The Eagles are drastically outperforming other teams in all metrics, but especially in two tries scored. Based on how everyone else performs, you'd expect the USA to be 2-8 ... instead they are 8-2.
Why the Bad
The reasons the Eagles are not scoring tries are myriad, but here are a few reasons:
1. They don't do offloads. When every now and then they do decide to offload out of an attempted tackle they score. Sam Sullivan scored a try against Ireland that way. Ilona Maher scored the game-winner against Great Britain that way. But they do it something like once or maybe twice a game.
Instead, they go into contact and set a ruck ...
2. It's always a ruck. Almost never do you see a tackled USA WNT player pop a pass off the deck or pick up directly from a tackle and keep going or make a pass. The first player to a tackle sets the ruck ... always. This is a very conservative way to play. It means they usually keep the ball (unless it's France ... more about that later). But it also means that if it takes a while for someone to come in as halfback, the defenses have plenty of time to re-set.
3. You rarely see loops, which are an especially useful way for women's teams to extend the line. Instead you often saw kind of a rookie mistake whereby a player runs sideways, dragging defenders with her, and then passes to the wing, who now had three defenders charging down her throat.
4. On-note play calling. Throughout the Sydney 7s, the USA team was working on a straight crash off a flat halfback pass. The timing for such a play is very important, and was off for the USA team. They succeeded maybe half the time (probably less) and when they screwed it up, it became a turnover or at least a panic-stations moment.
France
And New Zealand, but this is more about France, because France, overall, is about the same level type of team. The French have figured out that the Eagles don't do anything flashy out of the tackle, so they counter-ruck ... hard. That produces turnovers and penalties. They also go very hard into the tackle because they know the USA players won't pass once contact is initiated. As a result, they get turnovers, they win the contact point, and the USA ends up looking really bad.
Players
So here's where we get into a weird aspect of this team. They are third in the World Series. They have reached the podium in all four events this season. And yet, there are problems within. Specifically, while some teams have consistency among their players—everyone is at least, say, a 6 out of 10 player with certain skills that are better than that. France, Australia, and New Zealand, and maybe even Ireland, or like that. (New Zealand's players are all 8/10 it appears.)
The USA is not. The USA team has some excellent players, and some who are not up to the level they should be. There is a consistent pattern of mistakes (bad passes, horrible clearouts, holding-on penalties, missed tackles) by specific players in this team. As a result, by the end of the tournament Ilona Maher has been ridden into the ground trying to make up for it. Not just her ... Kristi Kirshe, Sam Sullivan, Naya Tapper, and Cheta Emba too.
Great teams have value throughout. This team has holes, and that is one reason why they can't piece it together to score more than two tries a game.
This team also had supreme talent that has, by razor-thin margins, pushed the USA to 3rd in the World Series. But if there's an injury, or a little bad luck, or other teams emulate the French a bit more, this two-try house of cards could fall.