>>5398089Because if you only train with your body weight, you plateau at a certain point.
Those things keep you fit, yes, but gaining strength requires you to add additional weight and force your muscles to exert their power.
The ancient Greeks understood this too. Some of the earliest forms of barbells and dumbbells can be dated back to this time era.
The people who only do cardio generally look fit, but have little to no strength.
The people who only lift weights generally have upper body strength, but their legs and hearts are weak.
That's why most decent weight lifting plans include cardio, be it biking, swimming, running, etc.
