Small business owners do care about the health and happiness of their employees. But even if we pretend for a moment that they do not, it's a threat to the business viability if workers cannot afford to live within a reasonable commute. If rents continue to outpace wages, those workers will eventually leave the area or the industry. The article talks about the business impacts of people leaving in detail (loss of talent, reduced quality of service, direct hiring costs associated with turnover, etc).