It needs to sell well enough to provide an ecosystem where games can sell well and make Nintendo adequate profits.
Install base is not a direct measure of whether or not a platform is successful. A device that sells 30 million and earns the company a few billion in profit is far more successful than a device that sells 100 million and causes the company to lose a few billion.
When the herd loses its way, the shepard must kill the bull that leads them astray.