Either there are a ton of infected people who are experiencing mild to no sympomts OR the disease is not nearly as communicable as initially predicted. I guess there's technically a third option where there are both more asymptomatic people AND less spreading than predicted. I tend to think the virus is highly contagious and has been caught by many who already long since recovered and never realized what they had and there are just a lot fewer severe cases/hopsitalizations than predicted. Our testing can't yet identify those who already recovered and have antibodies and we're not sure about those who may be immune/less susceptible to getting the infection in the first place based on existing antibodies to combinations of other infections (we do have a pretty good idea about which groups experience the most severe symptoms when infected).