Why is Lonesome George considered the last of his kind when there are 20,000 more like him?

Lonesome George, last-of-his-kind Galapagos tortoise, dies

QUITO, June 24 (Reuters) - Lonesome George, the last
remaining tortoise of his kind and a conservation icon, died on
Sunday of unknown causes, the Galapagos National Park said. He
was thought to be about 100 years old.

Lonesome George was found in 1972 and had become a symbol of
Ecuador's Galapagos Islands, which attracted some 180,000
visitors last year.

"This morning the park ranger in charge of looking after the
tortoises found Lonesome George, his body was motionless," the
head of the Galapagos National Park, Edwin Naula, told Reuters.
"His life cycle came to an end."

snip

Some 20,000 giant tortoises still live on the Galapagos.

http://articles.orlandosentinel.com/2012-06-24/news/sns-rt-ecuador-tortoise-tv-pixl2e8ho4g7-20120624_1_female-tortoises-galapagos-islands-galapagos-national-park