Answer:
They were scared
Explanation:
Because
Religions: All the nations conquered by the Ottomans were converted to Islam. Europe was of course, Christian. It took hundred of years for Spain to be returned to Christianity. The European nations - or at least their elites - did not wish to be converted. I’d guess the peasants would have resisted - but as they were more interested in survival normally, who was ruling them was of little consequence.
Military: The nations of Europe were made up of hundreds of small states in the main. The concept of “nationhood” was not strong (the English were perhaps the first to develop this as a strong ethos) and those small states were continually warring one against the other. Very difficult to get these factions to cooperate to fend of the Ottomans.
