Question

Why might the Italian city-states have resisted the exploration around the world?

The discovery of new trade routes to the east threatened the city-state's control over that trade.
The technological innovations that allowed new discoveries were adding to the wealth of Italy's enemies.
The search for new Protestant converts threatened the power of the papal states and Rome itself.
The Italian city-states were fearful that new trade routes would raise the influence of Islamic empires.

Answer 1

The discovery of new trade routes to the east threatened the city-state's control over that trade

Answer 2

One reason why Italian city-states may have resisted the exploration around the world would be that "The discovery of new trade routes to the east threatened the city-state's control over that trade," since for most of the 1400s the Italians dominated the spice trade (along with the Muslims).