Explain why urban exclusion appears to be growing in large cities.

I thought along the lines of
large cities=large populations=larger observable spatial inequalities= more urban exclusion. Is this any help?

You have a good start. In the U.S., urban exclusion is compounded by poverty, lack of decent paying jobs, and the increasingly higher cost of medical care. Also, cities have lost many manufacturing companies, thus decreasing their taxes and forcing city governments to prioritize and make budget cuts.