People who exercise in the morning are usually energetic and like to start their day with a boost that will push them throughout the day.
Morning people like to get things done in the morning, which is why some of them prefer to exercise or go to the gym before starting their day. See What are the benefits of being a morning person
Working out or exercising in the morning saves you time during the rest of the day, as it becomes part of a daily routine.
Some people prefer to exercise in the morning to avoid getting lazy after a long day and skipping the exercise.
Some people like exercising in the morning as there are less distractions that can get in the way of their work out.
Some people believe that exercising in the morning burns more calories, as it raises their metabolic rate during the rest of the day.
The sense of accomplishment that follows a good morning work out improves people's mood, in addition to the release of endorphins, the feel-good hormones, that carries them the rest of the day. See What hormones are released during exercise
Regularly exercising requires strong self-discipline, especially if it's done in the morning since it requires more will-power. This provides people with a sense of self-discipline and strong will-power.
A study has shown that people who exercised at 7 am slept longer and deeper than people who exercised at 1 pm or 7 pm.
Some people find that starting their day with exercising regulates their appetite and allows them to make better and healthier food choices.
A study found that those who exercise in the early morning experience reduced blood pressure during the rest of the day as opposed to those who worked out in the afternoon or evening.
Some people adopt the habit of exercising in the morning as they find it healthy for their mental and physical health. See Reasons some people are addicted to exercise
Some people like to go to the gym in the morning so that they do not find the gym crowded. Many people prefer not to exercise in the early morning and as a result the gym can be empty during that time.