What does employees like working in socially responsible business mean?

It's means they like working in a business that contributes to society in a positive way, instead of a negative way. Business that don't solely focus on investment return for their stockholders, but balance the money making aspect with a commitment to taking care of their communities, environment, and so on, and don't just leave all of societies problems up to society and the government to solve. They have all the resources, (time, money, man power) to make a difference. Also, this looks good to consumers who might buy from a socially responsible firm as opposed to one that is not. A socially responsible firm also lowers their chances of losing some control, should any lawsuits come about, or if the government steps in and forces them to be more socially responsible.

And really, employees just generally enjoy working for companies that make a positive impact, more than they do working for a company that is either indifferent or makes a negative impact.