The Ancients didn't speak Arabic - the Caananite languages are similar, but then Latin is similar to French.
Of course they don't speak Arabic. Take a look at the artifacts and the travel habits, they are desert people. It's what they have in common. The desert is a key component of the gods they had chosen, the poetry they wrote, and the artifacts they left behind.
Then they're coastal nomads, not desert nomads.
But they were in the coasts of what is known as Arabia, they were desert people. You need dates you find a palm tree, fish you go to the sea.
Then along came a man, a man named Mohammed and he was like Attila who came before him, he unified a fractious and perpetually warlike people and he led them out of the desert and into better lands. Unlike Attila Mohammed also created/revealed a new religion to bind these people. Over the following centuries the subjects of this new ruling class gradually adopted the ways, language and finally religion of their masters.
Mecca was a center of trade between all types of cultures before Muhammad came along. It was not a homogenous society in the time of Muhammad. It is said that he is of Persian descent anyway. Even people at that time saw the dilemma, which is evident through the hadiths and pre-Islamic poetry.