Why an exam to pilot drones?
The shortest answer: simply because you use the airspace!
Install a camera on a remote-controlled boat or car, and you are not concern by this exam! But this exam is not so negative, it makes you officially a PILOT. It gives you a value and a framework to evolve your aircraft and allows you to be both protected and recognized.
The official knowledge requirements for the theory test involve knowing a lot of areas that will not be useful for everyone, but overall you will learn interesting things to better use your drone.
Was it really necessary to create this exam?
Yes, in particular to differentiate yourself from indelicate users who do insane flights! Keep in mind that in Canada, between 2014 and 2017, the TSB processed 30 pilot reports who saw a drone on their flight path, fortunately without collision.