Desires themselves are imbued with negative affect. As Naval Ravikant tweeted, "Desire is a contract that you make with yourself to be unhappy until you get what you want." More fundamentally, I think the very mechanism of how desires work is through negative hedonic tone. Contemplating and actually fulfilling the desire is associated with positive hedonic tone. The gradient between the negative hedonic tone of the desire and the positive hedonic tone of its fulfillment is how motivation emerges.
Long-term meditation is often associated with a lessening of the influence of desire, and greater happiness.
I agree. There is also a learned mindset; to treat desire as a lack or as a vision of fulfillment.
Personally, I think the role of meditation and happiness is in creating emotional/cognitive distance between one's self and the observed desires, not the lessening of desires, per se. Though it depends on one's path, I suppose.
Long-term meditation is often associated with a lessening of the influence of desire, and greater happiness.