Ultimately because it drives down the cost of labor by locking employees in.

Employer’s cost per employee is much much lower than an employee’s cost directly from insurer. The employer “sells” the benefit to the employee at a higher perceived cost because of this.

Without an employer’s discount, an employee simply cannot get the same insurance coverage.

Thus, the employee agrees to working pay and conditions which would not be agreeable without the pressure to get health coverage.

Hence, lower cost of labor to the employer and pressure to keep the current structure in place.