Why isn’t Europe and Asia considered one continent?

It sometimes is,and is called Eurasia. I think because of its size it is considered two continents.

Europe And Asia One Continent

The idea of a continent has a somewhat transient definition. It is sometimes considered one continent and called Eurasia.

When they're defined separately there are two general reasons given.

1) At the dividing line there is a mountain range that isolates the regions from one another.

2) Under the technical definition of "separated by water" there is a small river and stream system that does (kinda) separate the 2 land masses, at least seasonally. The streams are just too small to show up on most regional or world maps.

While there is a cultural divide at the mountain range due to isolating factors, it doesn't really have to do with racial terms like "whites" and "Asians" since it's a horrible line for separating people by skin color (see areas that fall into both continents like Russia or Turkey, and color differences between South West and East Asia).

The idea that the world has "continents" is an ancient one, and in Western Civilization, Africa was known to be a separate continent. In traveling from Europe to Asia, one had to cross the Mediterranean Sea/Black Sea in order to reach Asia Minor, from which there was unbroken land stretching all the way to China. Comparatively little early trade from the Mediterranean to the east was through the slavic lands north of Black Sea. Hence, it was easy for the early Western Civilizations to imagine that there was "three continents", which was later expanded to include Greenland, Australia, and the two Americas.

It's likely that had there been no Aegean Sea/Black Sea, so that there was a clear and easy travel from Europe to China, the ancient peoples might not have thought there were 2 separate continents.

Edit: If we allowed the "technicality" that we can consider formerly separate land masses to be separate continents, then the world has dozens of continents. India, for example, which rammed into Asia something like 10 million years ago. In geology and plate tectonics, they are called "sub-continents" and/or "terranes". Of course, the idea of continents ramming together wasn't even considered to be a fact until in just the last half century, so it can't be the original reason why Europe and Asia are considered separate continents.

First of all, there isn't a total concesus of how many continents there are in the world. In the U.S., we define a continent as a large area of land that has its own distinct cultural and geographical features. Europe and Asia are considered two separate continents probably because Europe's cultures are entirely different than the cultures of Asia.

<<I mean I’d understand if there was some technicality to this such as they are two continents that just drifted together.>>

As it happens, that technicality applies. The collision is marked by the Ural Mountains.

Absolutely. Europe is the center of the world, and they needed to be distinct from all of the savages. This also relates to the Mercator map projection, which portrays Europe as several times larger than it should.

BTW, technically Africa is part of the same continent, and both North and South America are one continent.

Europe ends at the Caucusus Mountains, hence Europeans are considered Caucasians