That’s part of the large variety of projected outcomes, you have no doubt seen all sorts of graphs describing “best case scenarios” and variations up to “everyone dies case scenario”. Those graphed variations are primarily based on how large a part of the population quarantine themselves so they can be grouped into the variable of people not spreading the infection.
Sick people currently undergoing treatment however can not be counted as non-contagious as they are coming into contact with medical professionals. Though they’re not as big a spreader as an asymptomatic person this is why the estimates are so greatly different, there’s a LOT of variables involved and all of them have pretty large levels of uncertainty. One thing we do know is that the dead are not going out shopping and a properly handled body wont infect anyone.