Why were Europe, Asia and Africa classified as different continents?The main reason is because they have very different cultures and histories, so most people count it as two continents, but sometimes it will be combined as Euroasia. The problem is, there isn't a clear detention of a continent, if it's "a large landmass generally separated by oceans" then Euroasia is defenitly one continent. But what about the Panama and Suez canals? Huey don't seperate the continents do though? So now we have Antarctica, Australia, The Americas and the monstrous Afro-Euroasia.
Then there's that word "large" without its ice, Antarctica is actually just a bunch of islands, and the largest is still smaller then Austrlaia. And is Australia a continent? Or is it just the mother of all islands? What about Greenland and New Guinea? They're big. So now we have two continents.
Ok, so how about we use "a continental plate" as our definition of a continent. We have the Acrican Plate, The Noeth Ameircan Plate, the South American Plate, The Australian plate, the Euroasian plate, ok this looks like a good definition. The Antarctic plate... The Arabian plate, the Indian Plate, the Pacific plate, the (off the coast of Chile) plate, the (just east of Japan) plate and still a few more.
So how about our detention is now "a Continetal plate containing mostly land" then we can include six continents.
Yes, they are one continuous land mass. But at the time they were given their respective names, no one was thinking, "oh, there are these three continents-what shall we name them?" At that time, no one had a clear view of how far any of them extended. All they knew was that, surrounding the Mediterranean Sea, there was land to the north (Europe), south (Africa, aka Libya), and east (Asia). These names therefore referred to the land found in each direction, and while they were called continents, the concept of continent was not as precise as the one we think of today. Indeed, many people believed that Africa connected not only to Asia at Sinai, but that India and Africa were connected, rendering the Arabian Sea a closed body of water.
In short, the ancients weren't thinking in quite the same terms as we are, but once a thing is named, the name tends to stick.
But you are not alone in your observations-this issue has bugged a lot of people over the years. Some actually assert that there are only four continents: Antarctica, Australia, America, and Afro-Eurasia. In fact, the combining of North and South America into a single continent is standard teaching in many Latin American countries. In other words, the debate rages on.
It goes back to how the Ancient Greeks and Romans visualized the world as they knew it. The landmass south of the Mediterranean Sea was called ‘Africa' for reasons not clear and the lands to the east of the sea were called ‘Asia' (probably derived from the word for sunrise). These names stuck in the imagination of westerners and they were retained even after the beginning of the modern age when explorations and expeditions afforded greater knowledge of world geography.
Proposers of Continent boundaries have used Geography and cultural differences for differentiating landmass from each other. It's done, no one likes to change now!
If your view is taken, then there will not be North and South America as separate continents either, because Panama region connects both.
Europe and Asia are culturally different although they lie on the same continuous tectonic landmass i.e. Eurasia. This is because Ural mountains, Caspian Sea, Caucassian Mountains and Black Sea forms a natural boundary which made Ancient cultures not to mix easily. Similarly, Thrace (Europe part of Turkey) is separated from the Asia Minor by Turkish Straits and so there is a definite difference and boundary between Asia and Europe.
Coming to Asia and Africa - both lies on completely different tectonic plates. The connecting Sinai Peninsula region between both the continents is very small compared with their landmass sizes and Geographically this tiny landmass can't make the argument in OP's favour. Except Egypt, Asia and Africa are culturally different before Islam.
the roman empire has defined those landmasses as they were seperated by water bodies.