Why were the Middle Colonies so diverse?

There are three main reasons for the diversity in the Middle Colonies as compared with the New England and Southern Colonies. The first and possibly the most important is the geography of the colonies. The Middle colonies benefited from having a very diverse geography, which lent itself to more economic opportunity than the other colonies. The Middle Colonies became known as the "breadbasket" for the early colonies. The soil was fertile, not rocky, and the hills were gently sloping, making the region perfect for certain types of critical agriculture. The climate is moderate with a long growing season and short winter. Grains like wheat and grazing animals like cattle were significant agricultural products produced. However, this was not the only geographic advantage.
The Middle Colonies had many places where open access to deep water and protected coves line the shoreline. Deep water allowed for numerous entries into the continent from the ports, and because of the milder climate, they were able to attract numerous immigrants from all parts of Europe.
The second reason is that the Middle Colonies were diverse in religious practices. There was a tendency toward being much more liberal and open regarding religious practice. This was probably the result of the diversity of immigrants attracted to the colonies and settled by Europeans.
The third reason is harder to document with hard evidence, but anecdotal evidence suggests the Middle colonies were interested in making sure there was at least a rudimentary system of education available to citizens. There were many efforts to develop a public education system. A strong foundation of education tends to result in people thinking differently about the world around them and tends to attract diversity. Progressive, tolerant attitudes are the result of education.