They're still the top dogs of the industry, at least in terms of iconography, going the distance, and harvesting raw, filthy profit. That can sting a bit if you're cheerleading Xbox or PlayStation alone (and I pity anyone who does). For a certain kind of gamer raised in the post-PlayStation climate and receptive to marketing pushing 'games for adults', they might wonder why Nintendo is still hanging around with their colourful, childish recycled games and gimmicky, underpowered, toy-like hardware rather than bowing out for a worthier successor to take the throne, or even wishing for Nintendo's failure in the hardware market leading to third party participation on more established hardware. As a 40+ gamer, I'm old enough to remember a time when the same demographics queueing up for CoD today did the same for Nes, Game Boy, and Super Mario Bros 3 decades ago. The games are still the same, but gamers themselves have changed quite a bit.
Nintendo hate is a different thing from MS or Sony hate. Those individuals tend to subscribe to a tribalistic rivalry, a petty 'if you're not with me you're against me' antagonism we see everywhere, every day. Nintendo hate goes a bit beyond that, since it's largely perceived to be a different market, even a niche one, but some gamers really, really have it in for Nintendo nonetheless, often for a bunch of reasons. It's a shame.