Why do some universities force their professors to perform researches at least once a year?

A University forces a Professor for research because firstly it encourages the faculty to discover something new by research which beneficial for humanities, secondly research encourages to know and become expertise in research world, thirdly it increases the university research level on peak to obtain more attraction from journals as reviewers.

To keep him update with the new information and technologies with the world  

the important universities are interested to develop and to reach a situation where their students can get the Bachelor certificate, then the Master and the doctorate

the amount of researches and the number of experience's years a teacher have, increase his rank and allow him to supervise the Master message and than the doctorate

 

Because firstly it encourages the faculty to know and become expertise in research world, secondly it increases the university research level on peak to obtain more attraction from journals as reviewers.