Everyone can agree more or less than Nintendo's own games sell best on their hardware. Many would argue that Nintendo's own games are The reason to buy any Nintendo hardware.
As a result, 3rd party games on Nintendo platforms are secondary at best with very few exceptions. As a result, the vast majority of 3rd party games have a more limited market than they might on other hardware platforms, or at the very least, the games can be expected to sell fewer units than they would on other platforms.
In short, it's generally more profitable for 3rd party developers to focus on other platforms where they aren't competing with the primary reason most of the installed user base is playing on a Nintendo platform.
Is it biased when they regularly and deliberately divert more effort and resources to other platforms? By definition, of course. But it doesn't take a stretch of reason to see it has more to do with seeking an optimal ROI than some sort of personal, emotional grudge. That's generally how biased consumer minds work, not the companies that develop and publish games as an investment looking for the maximum returns.







