When discussing a question such as this one, it is useful to keep in mind the role of contingency in history, and the degree to which historical events are never preordained. Furthermore, keep in mind that the Arabs actually did reach as far as into France in their initial expansion, a fact that can be seen in the Battle of Tours, with Charles Martel's defeat of an Umayyad army (a battle often regarded as one of the key watershed points in Medieval and European history).

That being said, I suspect other factors would have played a key role in this as well. Most importantly, you should look towards the internal fracturing of Islamic politics and power, as well as the fundamental geographic challenges and limitations of exercising control over as vast a span of territory as that conquered by the Muslims in these initial expansions. Such rapid expansions will always eventually hit a limitation, given the strains on manpower and resources involved in conquering and holding these various territories.

Furthermore, however, the rise of the Abbasids could be understood as a contributing factor as well, because, when they overthrew the Umayyads, the lone survivor of the purge relocated to Spain. Thus, we see the Islamic world already beginning to splinter, with the Abbasids, centered in Baghdad, opposing a rival Umayyad Caliphate centered in Córdoba (a caliphate that also would have had to wrestle with its Christian neighbors eager to recapture the territories lost). When the Spanish Umayyads themselves collapsed in the early eleventh century CE, it had the effect of weakening Islamic power in Iberia, to the advantage of their Christian adversaries.