The Big 3 have nothing to do with wagon sales in the US, Volvo have always sold at least 1 here until last year because people were to busy busy buying crossovers and SUVs.
And the Big 3 probably wouldn't need any crossovers if wagons sold well enough, but they just don't. That whole thing started in the early 2000's because SUVs with their size gave a perceived safety that prompted many of our parents (my mother included) to buy them, even though they are not safer due to a higher risk of rollover due to the significantly higher center of gravity.
Wagons did once rule the market, but the children of the buyers shunned them when minivans came around, then those children shunned them for SUVs, and now those children who now are adults will likely shun them for something else.