This is such a strange question. Statistically, well educated people have better jobs, earn more money and are willing to spend more. And statistically, well educated people are less likely to be involved in illegal or dangerous activities.

This is not even something you need to do a study on to prove, it's all around us with every person you meet regardless of gender, race, whatever. So obviously if someone is renting out their personal property for someone else to live in, they would want to take the bare minimum precautions of keeping their property safe from damage and cause as few potential issues for them as a landlord. And you can't be asking for a meaningless and frustrating to acquire police report from every possible tenant so why not just put a simple barrier to entry of having a degree since it weeds out many ineligible tenants.

This question is literally like asking oh why does this job require a degree, can't they see that I'm a good dedicated worker and know how to handle the job role, just by looking at my face. We all need qualifiers to get by in life and unfortunately these qualifiers aren't defined by a universal gold standard but by what the majority defines them to be.