I've heard this so many times from people in my circle, but then they'll ask to play Mario Kart when they're at the crib. To all the people who say Nintendo fell off, to me, they're the ones who have changed. As you get older your tastes change and you want to experience more. For a lot of people Sony and Microsoft offered them something new, but at the end of the day Nintendo continues to make great games with iconic franchises.
I don't really consider Nintendo a nostalgic brand or king of nostalgia because they are very relevant today... similar to Nike/Jordan brand. Most people fell in love with the company back in the 80's/90's and still purchase their iconic retros, but they are very still considered trendsetters in their industry. And for that reason I feel Nintendo are the trailblazer and trendsetter for gaming . They continue to innovate and move the industry forward while staying true to their roots.
Do they make mistakes, sure... but throughout the years they've demonstrated that they are all about quality (something I wish Nike still did) and great experiences . If you grew up with the NES or SNES and you've played a Playstation or an XBox you eventually long for those quality experiences you once had as a child when you first started gaming. You begin to realize it isn't about the characters or graphics, its the passion Nintendo puts into their IP's. They know how to make fun games. That is the only thing that matters.