Because they want the best employees to work for them. Employee compensation is a part of the expense of doing business for every business. Some businesses believe that sharing the wealth builds a stronger bond with the community and increases the chances of survival for their business. Other businesses believe that offering goods or services at a lower cost to the community by having lower benefits to their employees is the way to go.
A perfect example of why is a company here in NC called SAS. They are repeatedly named one of the best companies in the country to work for. They offer a multitude of benefits/percs to their employees AND the consistently post terrific profits and have virtually no employee turnover.
These are good employers with good employees. It is physically responsible too. It costs both the company and the employee a lot of money for good insurance but its well worth it if you get sick. Went to the ER via ambulance recently. Bill was $700 for the ambulance and $8600 for a couple of hours lying on a gurney in a hallway, 2 Meds, and an MRI. Ridiculous.