I did some simple google searching as well, and while it seems possible to transmit the virus without symptoms it also seems that a small minority of cases are

I did some simple google searching as well, and while it seems possible to transmit the virus without symptoms it also seems that a small minority of cases are transmitted by asymptomatic carriers. The numbers I find are ~20%. Sure, that isn't negligible, but I can understand why experts would base a strategy on those with symptoms.