Here's a couple of accounts of Pope Urban's call for the Crusades which sort of give's you perspective on their reasons.

Regarding the religious basis of the crusades, there are arguments made that there were geo-political reasons for it. The main thing is that the Islamic Caliphate is not the biggest instigator of this event. It is mostly considered that the invasion of the Seljuk Turks into the Levant and Anatolia was an important cause. The Seljuks sacked many important pilgrimage cities and Greek territories, and they were much more hardline than the previous Islamic owners, especially in regards to the privileges and access for pilgrims. The Pope called on the crusades for the assistance of the Byzantines and the capture of the Holy cities of Christendom. This is evident when we read the secondary sources regarding the first crusade, as they formed together in Constantinople and then moved into Anatolia to capture some Turkish controlled cities, before moving into Syria. Of course this is after looting and attacking Christian cities and Kingdoms, and just, terrible management.

Source: The History of Medieval Islam, JJ Saunders, Barnes and Noble, 1965

In my own opinion, while it is true that looting did enhance the wealth of some kingdoms which took part, and groups like the Templars did very well for themselves, the original call for a defence of Christian empires against non-believers, similar to the reconquista in Spain seems like a much more valid reason for excursions. The Sultanates of the region were just much wealthier due to trading institutions, and the economic invigoration of europe by the crusades was simply a by-product. While it is true that there was some cynicism within some people within the religious and secular leadership, it should be understood that people did believe that the religious and political reasons were just.