Because the employer is running a business. And HIS customers are looking for the best value for THEIR dollars. What some college kid is being paid is not not their concern, and to the employer, employees are an expense, and your personal problems with money are not his concern.
Lessee - I can to to the McDonald's in one place and buy my lunch for $7. Or I can go to another place, say Wendy's that pays their employees $30/hour, and buy my lunch for $40.
Really, which place do you think I'm going to go?