For most questions in biology when you ask "why is X ok but not Y" the answer is usually always scale. Because Y is too much.

When you exercise your body will tell you when you are pushing it too far, when your heart rate has been too high for too long. When you have to stop and take a breather for a minute, your heart can also take a rest and the heart rate can come down.

Energy drinks however stimulates the heart to go full throttle for hours, with no breaks or rests. Often with no purpose or gain. It's too much