Here's what I put to give anyone an idea.
Whitman might have left out the grand and wealthy people in America because they already had everything. They had no reason to hope for a better country when they were sitting pretty - and neither cared about togetherness because they were wealthy and own everything. This is found when Whitman states "Each singing what belongs to him or her and to no one else ...". The wealthy figures are not included because they are not singing. They do not hum while they work because they do not work.