Why do think most of major cities were along the ocean or major water ways ?

Being along oceans or major water ways made trade to other areas more accessible, which attributed to those cities' economic and financial growth.

Waterways were used a lot in the older days as a mean of transportation. Now it used mainly for shipment across the country. New York was built in order to draw in people. The water provided an easy access for them to get in, and it also helped sustain the economy of the city. Water provided jobs, trade, and immigration. 

No one knows sorry. : )