well id say ...
1. people went on Crusades because they wanted to take back Jerusalem by reason that they thought that it was rightfully theirs since it is there where Jesus died.
2. some people did it for honour, revenge or love.
3. the people wanted their sins to be forgiven, to go to heaven or to take back goods from the Holy Lands or because they had committed a crime and were forced by the church to go on a Crusade.
and 4. some people just went on Crusades for fun.
