Why were people peasants?

Answer 1

They weren't. In Europe in the middle ages the closest thing to a slave was a serf. A serf was owned by the estate and so was his whole family, but they weren't slaves in the true sense of slavery. A peasant was a poor person, but free to move about and to change locations or jobs.

Answer 2

Most peasants did have freedom. The only ones who had no freedom at all were slaves, and in much of Western Europe, slavery was either very limited or absent. It became illegal in England after 1102, for example, but was already uncommon at that time because the Church often condemned and tried to end it.

Peasants were of different types, and the different types of peasants had different kinds of freedom.

In many places, the lowest level of peasants were serfs, who were tied to the land, as they say. This meant they were not allowed to move off the manor. But in exchange for the freedom they lost by not being able to move away, they were given the right to live on the manor, to farm a part of the land, and to be protected by their lord. They had a specified amount of time they worked for the lord each week, usually one or two days, and they farmed in common with other serfs for a similar amount of time, but what they did on their own time was up to them. This system actually dated back to the villa system under the Roman Empire, where the coloni were tied to the land. We see the unfree status of these people today, and tend to focus on that, but we should remember that during wars and famines, many people gladly gave up freedom in exchange for the protections of the manors.

Some peasants were freemen. They might or might not have lived on manors, but were more free than serfs. Those who lived on manors were tenants, who paid rent instead of working set amounts of time, and were allowed to leave the manor. The down side of this was that they could be told to leave, if the lord wanted to get rid of them for any reason.

Other free peasants were yeomen. They had their own holdings and did not live on a manor. They were not entirely free, because they were obliged to do military service, if the king required it, and they had to pay taxes.