Why did the monks and friars own no land?

Most monasteries did own land, but it would belong to the monastery rather than to the individual monks. Monks would farm the land and grow their own food etc. Many monasteries produced their own wine, and some still do. Some monasteries owned large estates. Many monasteries eventually became very rich, and the monks were no longer living the lives of simple poverty that had originally been envisaged when the orders were started.