Because a 10 arc minute shift in the Moon's sky location as seen from Earth is enough to make a total lunar eclipse become a partial or 'Umbral' eclipse. At a distance of 240,000 miles, 10 arc minutes worth of parallax from Earth will obtain if you shift your location on the Earth by only 700 miles. It doesn't surprise me that observers on the west coast of North America saw a very different eclipse than observers on the East Coast some 4000 miles away!