>>Is it because he was first to publish?
In short, yes: Vikings arrived to America a lot earlier, but they did nothing about it, so much so that for a long time archeologists were not sure whether it had happeded at all. Basques and even Chinese may have reached America before Columbus, but again, nothing came out of it.
The Spanish Crown was the first to actually do something with this knowledge. What they did is certailnly no cause for celebration, but it did change the course of Western history.
As a related tidbit, I realized not long ago that many people from the USA, even people I consider well educated, actually believe that Columbus reached the coast of the US on October 12th, 1492. In reality he was never near what we now call North America.