Why is cycling so happy?

Could you elaborate on the sentiment expressed in the phrase 'Why is cycling so happy?'? Are there specific factors that contribute to the joy and happiness often associated with cycling? Is it the physical exercise, the sense of freedom and independence, the connection with nature, or perhaps the social aspect of cycling with friends or in groups? I'm curious to understand the underlying reasons behind this popular sentiment and how cycling can positively impact one's mental and emotional well-being.