Microwaves aren't Faraday cages as it's too difficult to manufacture a perfect seal, instead the size of the holes in the door act as a tuned RF choke.
People sometimes like to watch the food being cooked, for one. At KW levels of power a few dB is still enough to do harm. Lots of nasty reports in the medical literature of this type of exposure, typically unlucky repairmen.
The eye has very poor heat dissipation mechanisms, and they showed in the 70's the RF exposure could cause cataracts in rabbits. (I think dogs were exposed too -- it was a new field, so they didn't know what would happen)
