I like this article but this is actually a good point. "The rich" is mostly used in a negative way.
I'd argue this is because most attempts to reduce large groups of people to an idea like "the rich" or "the poor" are done in bad faith.
A support of this would be, within academic sociology or economics these terms will be used in a non slur way and it's because they actually have a reason to be thinking in terms of these groups instead of throwing them out as stawmen for some argument