Because it is not just a respiratory infection. The respiratory symptoms known as covid are caused by an immume system dysfunction. One of the functions of the immune system is to destroy infected cells. This causes inflammation. When the immune system is functioning correctly it regulates this inflammation by following up with a healing anti inflammatory process. SARS-CoV-2 attacks the immune system directly and causes an uncontrolled increase in those dangerous inflammatory processes, this is called a cytokine storm, it causes widespread tissue damage and it is the reason for the covid respiratory symptoms. At the same time as all that, the virus is also infecting the cardio vascular system, the liver, kidneys the gastro intestinal system and even the brain. This causes unseen longterm damage to those organs that results in myocarditis, hepatitis etc.