21 days of wandering around town touching stuff, coughing, serving meals, etc. before even showing symptoms. That’s a lot of door knobs for each person. And then multiply it by 6 (people sitting next to the guy), or 150 (the entire plane load).
Not to mention possibly vomiting and having diarrhea in the restroom on the plane, and the fact that Ebola can live in dried material on a surface for several days.