Speculating, but early identification, containment and tracing movement of infected patients seems to be the only way to stop the virus. In some cases, that means tracing two weeks of movement for infected patients. Italy was unable to get ahead of it.
Unfortunately, it's quite likely that infected people are traveling from high risk areas (China, Iran, South Korea) to other areas because they expect better health treatment.
For example, an infected 34 year old Iranian woman flew from Iran to Qatar, Denmark and Toronto on Feb 25/26. She traveled business class, was not wearing a face mask, and then took a public shuttle bus to the York Region. She reported the illness on Feb 27.
I think it's quite likely that she booked last minute flights because she was sick, and perhaps believed that being sick in an area with few cases is better than being sick in Iran. Imagine all the people she encountered during her travels, knowing she was sick, and all the planes that were not disinfected after she spread germs on those planes. Her priority is her health, with no concern for anyone else.