How was the Medieval Era a time of little change for peasants?

In the feudal era - from around the time of 1066 to ca 1400 the peasants owned very little and were engaged in subsistence farming, that is they produced what they needed to live on and generated very little excess. What they did make over and above their needs was traded for stuff that they didn't produce themselves. Additionally they had to pay a tithe to the Church, this was a tax of 10% of their harvest. Although they had some latitude to farm for themselves what they mostly did was to work for the local landowner - consequently most of their work was for other people. Feudal society was very restrictive, the peasants were tied to the land and would have to get special permission to leave their area. There were few if any chances for social mobility and as above the economic restrictions meant that they were not able to generate any meaningful wealth. In time of war they might also get summoned to join the an army which although it came with risks could allow them to earn a regular wage and there was the chance of plunder as well. But the risk was disease or violent death.