Why weren't slave ships allowed to dock at port?

Due to the fear that they might've spread diseases.

Explanation:

There's a widespread perception among Europeans at that time that African people have a higher tendency to carry diseases that's not many doctors in their country familiar with.  So , they never let slave ships to dock at a port. They're afraid of the "contamination".

Their suspicion often supported with the fact that slave ships usually smell really bad. They believed it's something related to the disease.  But that's not case. Slaves were chained down to the floor for months during the journey and forced by the slave traders to "use the toilets" right where they sleep. It was horrible. That's where the smell came from and People at that time were very ignorant about this fact.

Answer;

Access to important rivers and the Atlantic Ocean played a big role in their success.

Explanation;

Jamestown, the first permanent English settlement in the new world, was founded by a joint stock company anxious to return a profit to investors.

Jamestown offered anchorage and a good defensive position. Warm climate and fertile soil allowed large plantations to prosper. Plymouth, on the other hand, provided good anchorage and an excellent harbor. Cold climate and thin, rocky soil limited farm size. New Englanders turned to lumbering, shipbuilding, fishing and trade.