From 1150-1350 English land returned about 10% of the purchase price each year in rent. After the plague, from 1350-1600 real returns were about 6%. Rented land was a relatively safe and easily managed investment. Other investments required a higher rate of return: the London orphan's court charged 10% interest for commercial loans to merchants with sound security. Building rents would also be higher because of depreciation.
Thrupp, Sylvia L. 1976. The merchant class of medieval London, 1300-1500. [Ann Arbor, Mich.]: University of Michigan Press. p. 107