Why did France's overseas trade suffer during the French Revolution?
First of all, you should probably look in your own text for this because different texts can emphasize different things and what I think is most important may not be what your text's author thinks.
To me, the most important factor that harmed France's overseas trade during the Revolution was the fact that the Revolution really hurt France's domestic industries. In order to sell stuff to people overseas, you have to make it first. France's "manufacturing" sector was really tied in to the old order and so it was seriously disrupted when the Revolution started to destroy that old order. Since it was disrupted, there was less in the way of goods for France to sell overseas.