The techno-optimist in me says because I want to force them to improve their underlying models. When their engineers notice that their model struggles with weird edge cases that I purposefully mislabel (e.g. when prompted to select images containing motorcycles, I also pick a mountain bike with fat, motorcycle-sized tires), perhaps they will contemplate how to rigorously encode the concepts of “motorcycle” and “mountain bike” into their model, rather than simply pushing an abundance of training data through a black box classifier and hoping that by adding more crowdsourced data, it will eventually arrive at the right answer.

I think it's reasonable to believe that real self-driving cars are not inevitable, or even if they are, deliberate disruption of this process is healthy; e.g. it shouldn't rely on something this dumb.

edit: I get twice as angry when I have to fill in captcha in a service that I pay for.