Why did they add three feet to mount everest?
Himalayas are ever shifting due to collision of Indian tectonic plate with the Asian plate, the very reason why we have these mighty mountain range. As the Himalaya grow high due to the tectonic push, it also falls down under its own weight. This fall allows Himalayas to grow side wards too.
There's good evidence that the Himalayas, which Mount Everest is a part of, are getting taller, at the rate of about 5 millimeters a year. That's because the tectonic collision that created the Himalayas 50 million years ago is still happening today.