Broadly speaking, American business rewards scale and duopolies, while Japanese business is full of niches that trade efficiencies and global competitiveness for independence. This means Japan can have financially viable small-run toy lines.
In the US, a few buyers wield disproportionate amount of power over manufacturers. If Amazon or Walmart (and formerly Toys R Us) doesn't want your toy, it's not getting made. When they do want your toy, they want it at such a high discount to them that you must manufacture tens of thousands of units to make a profit. They may even want creative input in your product line. The buyers are part of the reasons why Transformers doesn't have a Sari figure, and why Green Lantern got cancelled.
This imbalance of power can even be seen in comics. In the US, publishers sell their books at 60% discount to the distributors. In Japan, they only need to part with 40%, and their market is healthier and more diverse because of it.