The point makes sense when you think about the examples given: workplace fashion and unspoken rules. A company dominated by people wearing "rich casual" would

The point makes sense when you think about the examples given: workplace fashion and unspoken rules. A company dominated by people wearing "rich casual" would benefit by explicitly embracing other casual fashions, such as various "poor casual" styles like track suits. This would let the non-rich-background people stop spending energy learning "rich casual" fashion. They could then spend that energy on things that actually help the company.