Nintendo takes advantage of certain aspects of human psychology in order to make you think you're having a good time. This is irrespective of the quality of gameplay and is widespread among all major Nintendo exclusives. The following will be a line of evidence proving my point and I hope you come out of this with a changed perspective.
Evidence 1: https://www.ncbi.nlm.nih.gov/pubmed/3346809
This psychology abstract dating from 1988 indicates that the human brain has biases towards lively colours. Athletes who wore bright colours had less fouls called on them and were viewed less negatively.
This is backed up by further research that baboons have bright colours in order to attract mates, therefore evolutionary pressures have made us particularly receptive to colourful objects.
Every major Nintendo exclusive has a colourful palette and EVEN THE CONSOLES THEMSELVES incorporate this brainwashing technique. Not convinced? There's more.
Evidence 2: The infancy hypothesis
The infancy hypothesis is a sociological work by Scott R. Hemsworth, published in the early 20th century. It states that people are naturally inclined to favor elements that hint towards their childhood; when things are carefree and simple. It has since become a staple of sociology and psychology.
Nintendo's games all contain very clear childish elements. They are all made to appeal to your inner child which psychologically brings up feelings of comfort and happiness (even if you aren't actually having fun). Due to this, the game can literally trick you into thinking you are having a good time. I have proof of this in evidence 3.
Evidence 3: Real life data
I went out to my neighbourhood and gathered a sample of 20 people. I showed them a black-and-white footage of a gory video game, then I showed them colourful pictures of a childish game. A whopping 18 out of 20 people preferred the childish colourful one. They couldn't exactly say why, but all their responses hinted towards implicit psychological cues. When I controlled for gameplay mechanics by showing them a mature game with similar gameplay to the childish game, they didn't like it. Therefore these effects were entirely irrespective of the actual gameplay.
I understand you may be in denial, which is natural because I will repeat: these are implicit cues. Nintendo is taking advantage of the hard wiring of your brain in order to trick you. This is not fully under your control, however there is something that you can do to avoid this.
The next time you are playing a Nintendo game, sit back and think to yourself, are you REALLY having fun? Or is your brain just telling you you're having fun?
I hope that this has enlightened you as much as it has enlightened me, and I wish you luck with the rest of your day.