Leftists especially only get a very stage managed experience where they only meet certain types of migrants like Mohammed who runs their local corner shop.

This. If you live in a middle/upper class life, you are going to associate with middle/upper class people, regardless of their ethnicity.

There's an incredible amount of mirror bias in liberal thought. They really believe that most people think and act like them: law-abiding, rational, good citizens. That's probably why it's so easy to convince them that "systemic racism" is responsible for all the blacks in prison. In their minds, everyone would be leading a similar successful life if only these poor unfortunate souls been given the same chances they had.