They have strong market share. GM is still #1 here and in the world overall (though just barely). Market share isn't their problem, it's that they have to sell at a loss to maintain it.
The reason Toyota has all but caught up isn't that they're particularly innovative, it's that the Camry can have $2,000 worth of better build quality than the Taurus or Malibu. Same with Corolla vs. Focus.
Japan gets to choose to either build the same cars and sell them cheaper, or build better cars and sell them for the same price. It's hard to win market share in that scenario.
The reason Toyota has all but caught up isn't that they're particularly innovative, it's that the Camry can have $2,000 worth of better build quality than the Taurus or Malibu. Same with Corolla vs. Focus.
Japan gets to choose to either build the same cars and sell them cheaper, or build better cars and sell them for the same price. It's hard to win market share in that scenario.