People find it easier to follow rules rather than principles.

The 10 commandments tell you what to do/not to do. The Beatitudes offer values and require interpretation to put into practice. They also are more ambiguous in their punishment/reward on the physical/spiritual level.

Compare:

"You shall not murder. You shall not commit adultery. You shall not steal."

vs

"3 Blessed are the poor in spirit, for theirs is the Kingdom of Heaven. 4 Blessed are those who mourn, for they will be comforted." ... "25 Woe to you who are well fed now, for you will go hungry."