It seems like the Middle East, North/East Africa and South/West Asia all have a history of Islam being a popular religion but East Asia, South Africa and Europe do not. Although I can understand the first two were far away and had little cross-cultural contact, why would Europe, especially Southern and Western Europe, never see widespread conversion or adoption of Islam if only because of trade and population movement?
What do you consider a foothold?
Large parts of Spain were under muslim rule for 800 years. Sicily was in muslim hands for two centuries. Large parts of what is now Russia were muslim after the mongol invasion and their conversion. On top of all of that you have the balkans were the Ottoman Empire held vast teritories for 500 years. Even in the modern period you have two muslim majority countries in Europe with Albania and Bosnia.