There is not an abnormally long incubation period** (mean 5 days, range 2-14 days, a couple dubious outliers), and WHO strongly disagrees that asymptomatic transmission is responsible for any meaningful fraction of cases. And "new cases in countries" is an irrelevant metric. The problem right now is not enough cases in certain locations where you know they should be catching far more people.
** A typical flu or cold has a 2-3 day incubation period, so it's longer than average, but again, I wouldn't use the phrase "abnormally long".