The USWNT has been dominant for so long because US women generally have had more opportunities to play organized sports than their foreign counterparts. However, as these soccer savvy nations take women's international soccer more seriously, they simply plug them into an already mature development model used for the men; something the US currently lacks. The rest of the world has caught up and some are starting to pass the USWNT by.
This could likely be the last World Cup the USWNT has a legitimate chance to win for some time.