Cardio can be tough on the body, especially the joints. Running in very hard on the body. Our ancestors most certainly only ran when chasing food or being chased. Some people are built for running while the average person benefits more from exercise like HIIT and speed rope. To train the cardiovascular system, short intense bursts are key.
The reason for this is simple. The focus of this type of exercise is the heart, lungs, and vascular system. These systems are autonomous (meaning they function in the background and require no direct action to occur). Unlike muscular training that requires focus to move a body part, the heart and accompanying organs, sustain their function without direct thought. These organs are constantly at work. They are beating and breathing when we sleep and go about the day. To make them stronger and more efficient, intense intervals, with rest periods in between, are the truest way to succeed in advancing their capabilities.