There are several reasons. One would be the introduction of luxury goods (as a result of the Crusades). As luxury goods were introduced in Europe, lords and kings wanted goods
… like silk and spices. Towns started to develop and coined money was reintroduced into Europe. Towns gave serfs other options in life and undermined the authority of the lords since Kings granted charters to the towns. Also, as coined money was reintroduced so the lords and kings could buy luxury goods, serfs began to sell their goods rather than exchange them for protection and land in the manor and buy their freedom. The development of natural rights, started by the Magna Carta in Europe in 1215, began to introduce ideas that undermined the basic principles of serfdom. Another reason feudalism declines in the decline of Viking raids. A period known as the Great Warming allowed Vikings to travel North and West (toward Greenland and Canada) and attack manors with less frequency. Since serfdom was based on a system of protection, if protection was no longer needed because Europe was safer than serfs rely on their manors less. Also, the Great Warming coincided with the Agricultural Revolution where surplus food was beginning to be produced. As a result of more food, people were healthier, could leave manors or sell their food to then buy freedom. By the 1800s, only Russia still has serfdom and it is outlawed by 1863. There is no single answer to this question--you may want to narrow to a part of Europe rather than Europe as a whole. (MORE) 
