...that part of the legs is very sensitive. People usually cannot stand the cold in that place for even a couple of seconds, while the jugular area is much less sensitive. The inner part of your legs is somewhat difficult to reach, cooling and walking is impossible, and you'll get funny looks if you dump soda cans in your pants (even Doc gets those from Roger!). And while you can get body temperature down rather well at that location, the jugular gives instant relief for the brain area, which is where the "initiating shutdown sequence" command comes from.
So yes, the blood vessels in the legs are big and transporting large quantities of blood, but the jugular scores 4 to nothing in sensitivity, accessability, social acceptability, and physiological effect.