If the issue is you want more fleets sailing...... this is actually on the bottom of the list of things to do.
#1 get rid of the players resource market. Force plantation owners to bring in their own supplies.... or add the contact shipping suggestion.
#2 same as above for the workers market.
#3 Get rid of plantations..... honestly, if you think about it, plantations basically killed normal trade routes.
#4 Promote piracy not try and destroy it. Give merchants a reason to sail escorted fleets again.
I know none of these are going to be acceptable options...... instead we just deal another hitt to pirates in a PIRATE game.