More energy for daily tasks. If you feel tired and listless during the day, it's hard to imagine that performing more work in the form of daily exercise can make you feel more energetic. More social opportunities. Endurance sports are social sports. Running events attract thousands of participants and the party after the event is a great time to meet people while you relive the race.
Cycling is a social sport and group rides are a tradition.
A brighter outlook on life. In classic research from the 1970s, William Morgan, Ph.D showed that moderate endurance activity increases feelings of vigor while reducing apathy and aggression. Running and walking have been used successfully to treat mild depression. There's nothing like getting out in the fresh air and sunshine for a brisk walk or ride to clear the mental cobwebs.