The main reason for the inability to build wealth among peasants during the feudal system was primarily due to the structure of the manorial system, where peasants were tied to the land and often needed to give a large portion of their earnings to their lords.
Thus, the most relevant response would likely be:
Peasants were required to tithe 90 percent of what they earned to lords.
This reflects the heavy financial burden on peasants, limiting their ability to accumulate wealth.