Because it was discovered by an advanced culture that was able to actually DO something with the land. After thousands of years of habitation by people who were still living in the stone age in the age of the Enlightenment has earned Columbus the honor of having discovered the new world.
Let me guess. You're not a history buff.
Not only did he NOT "discover" the 'new world' - he already knew that North and South America was here. He knew the history and had the maps.
The Vikings had a community of 30,000 in Greenland 1,500 years before Columbus. Leif, son on Eric the Red, sailed up and down the north American coast - they had winter camps in the south of of Cape Cod and explored up the Hudson, sailed the length of the continant - had a loosing battle with the natives on the shores of Mt.Desert Island in Maine.
The Vikings used maps by Zeno, of a family of cartographers.
A hundred years before Columbus "sailed the Ocean Blue", Sir Henry Sinclair, 1st Earl of Orkney (Scotland) sailed with a large fleet of ships to land he ALREADY owned in Nova Scotia, to establish a place to live out of the encroaching reach of the English King.
Columbus married into the family of descendants of Zeno - remember him - and knowledge of prior voyages and the continents, and, it is postured, maps.
He set out to sail BETWEEN the continents and thus to the back end of the spice rich Indies...not knowing that Central America was in the way. Indeed, he first encountered the islands and thought he had made it to the Indies - and thus, even now, we refer to the Native Americans as "Indians".
All that was before he launched a genocide, wiping out countless thousands of "Indians" = slaughtering them any way that came handy - being torn apart by his mastiffs or burned on stakes.
His third voyage ended in his being taken back to Spain in chains, on the order of the Queen.
Those are just some highlights.
So just why do we teach kids that he discovered America? And why do we so honor him?
It's akin to all the decades the schools taught, come Thanksgiving, and some still do, with school kids dressed in black and white - that the Pilgrims wore black and white clothing, erroneously mixing them up with the Boston Puritans...
The real histories are available. I'm not amused that even teachers don't get curious enough to do a bit of research on what they teach.