Because you are demanding an education to qualify to your job. Thus, you have zero excuses to pay me, or someone else what you would have to pay to uneducated and non skilled. None, except abusing the situation.
I'm educated, and if you want to hire me, you need to pay what is the minimum for me. It is higher than to person who never even heard of the field. Considerably. Or you hire someone without education, which no one does.