Basically, imagine that NASA is an inefficient huge gas guzzler - say, a Hummer. Imagine that ESA is a small fleet of more gas efficient but boring compact cars - say, a Saab representing Sweden, a Volvo representing Germany, a Fiat representing Italy... you get the idea. Let's say there's about 11 cars, plus a bicycle from Canada I guess. Now, somehow stuff all those cars into the Hummer, put a rocket on it, and launch it to Mars.
You forgot to mention that Canada is also sending the cool robotic arm that drives the rocket.
It is not for me to attempt to fathom the inscrutable workings of Providence. -- The Earl of Birkenhead