I've been reading quite a few books upon the Crusades, and although they give many different views (And I shall link them later), they each also hold similarities.

At the time of the first Crusade, The Fatimid Caliphate ruled Jerusalem, and under the Fatimids, Christians were persecuted, and were also numerous. The Christian populace cried out to the west and the Pope answered.

There were many reasons relating to the launch of the First Crusade, or at least at this point in history the term 'Crusade' would come in far later. It was seen as a great pilgrimage to rescue the holy places.

Pope Urban II preached the ideals of the first crusade at the Council of Clermont. Now if you think at this point of history most of Europe was heavily Christian, and the Papacy had unquestionable power. The idea of 'Holy' war, in that war can be sanctioned by the Pope for the rescue of the holy places, was quite an opportunistic prospect to people, both Lord and Peasant alike.

On the one side, Lords look for the liberation of the holy places for possible settlement (which they did), Chivalry (look at the effect Godfrey of Bouillon had on the ideals of Medieval Chivalry) and favour whilst others (Such as the 'Peoples Crusade', roused by a man named 'Peter the Hermit', who were later annihilated across the Bosphorus) found this a religious venture, for the Pope decreed that any that take up the cross must end their pilgrimage in the Church of the Holy Sepulchre, and death upon this Holy journey would grant remission of their sins. Thus it was quite the prospect to everyone.

The first Crusade was the most fruitful for the Westerners, as the County of Tripoli, the Principality of Antioch, the County of Edessa and the Kingdom of Jerusalem were set up over time. Trade boomed, and Outremer became a centre point of trade between the East and the West.

As crusades came and went, as Jerusalem fell and Orders such as the Knights Templar vanished due to supposed scandal, the idea of crusading against an overwhelming Islamic force began to change the mindset of people, especially when Acre finally fell in 1291. They may take Jerusalem, but they could never hold it or re-establish the Kingdom of Jerusalem, even if Acre still stood as a gateway to Outremer. Crusading is an extremely expensive venture, as Richard the Ist had to impose a 'Saladin Tithe' upon England, and Louis IX had to practically mortgage France to set upon the journeys of the Seventh and Eighth Crusade.

Crusades also started to be focused elsewhere, such as the Northern and Hussite Crusades.

So to stop gibbering on, I would say through my own opinion and research from books, that at the time of the first crusade, crusading was a prospect that could only increase a persons chivalry, land ownership, or indeed feed the peoples piety, but as the Crusades became less rewarding, military orders such as the Knights Templar died off, and Egypt became more focused, Crusading became extraordinarily expensive, and it waned until it stopped completely.

People of the First Crusade would be ecstatic to go on the venture, especially during a time where Egypt was most divided.

People of the later Crusades would incur the fines and taxation for seemingly fruitless campaigns when both Outremer was lost and the Ottoman Empire started to take full swing.

P.s. Please correct me if I am wrong in any of this, I thought since no one answered I would give my two pennies worth.