What caused many mountain men to become travel guides?

Due to the demand for fur decreased because of a change in fashion and beavers were nearly extinct, mountain men were responsible for several discoveries that made travel easier for people moving west

Mountain men is a term for male trappers or explorers who lives exclusively in the wilderness. They were popular and romanticized during the 18th century. They were vital in settling new territories and opening up new wagon trails that travelled through the North American Rocky Mountains due to their knowledge in the geography of the area. Later in life, many of these mountain men were hired by wagon companies and fur trading companies as guides or hunters.