New viruses tend to be more virulent than old ones. And new viruses tend to get less virulent over time -- else they die out. Ebola's incubation, transmission, morbidity, and mortality are such that it burns itself out. The common cold's are such that... it's common. Covid-19's are such that it's causing massive economic damage even if the recoveries are V-shaped. Hopefully covid-19 will get less virulent soon though.