My guess would be because two totally different civilizations developed at each extremity of the Eurasian continent and back whenever they decided what continents are, they just couldn't accept that such different things could be on the same continent.
While technically this may be true, there is a very obvious logical break between the two continents, especially when compared to Europe and Asia, which by the way botanists usually combine and refer to as "Eurasia" which is where most of the worst weeds in America come from. I'd vote with the botanists.
So, gringa, do they consider Europe and Asia two separate "continents" in Chile? A bit inconsistent, if that's the case, don't you think?
Perhaps the viewpoint is that all of N and S America is what was formerly called "The New World". Whereas the old world was already compartmentalized to its residents' satisfaction when the new world was "discovered".
The cabinet of the Maldives is holding an underwater cabinet meeting, using scuba gear, to make a statement before the climate control meetings in Copenhagen this fall. They are 7 feet above sea level and will be the first country to disappear.