This disease is insidious as it spreads early with no symptoms. Chinese travel all over the world. Early reports of the disease possibility were as early as Novermber in China. Then it took some time to recognize it as a ‘new disease’ in China. By then it was probably already spreading for a couple months worldwide with travelers. And five million Chinese left Wuhan worldwide on holiday before the lockdown began.
Basically… the recognition of a pandemic spread more slowly than the disease itself. By the time testing became available, the disease was already ‘everywhere’. Such is the nature of a pandemic.