Because most employees are not the 'customers' of the HR department. They are the 'product'. (The same way as viewers of a TV channel are not the customers of that channel, they are the product, and the advertisers are the customers, except that it is much easier to switch TV channels, than to switch companies.)

This means that the average HR department cares suprisingly little about pleasing the average employee. They will worry much more about pleasing management, etc.