Alma 51:8

Now those which were in favor of kings, were those of high birth; and they sought to be kings; and they were supported by those which sought power and authority over the people.

The people who wanted kings were from rich families. They wanted to be kings. People who wanted power and control over others supported them.

The ones who favored monarchy were from the upper class. They wanted to be kings themselves, and they had backing from people who craved power and authority over others.