Why piracy survived Roman control of the Mediterranean

How could pirates remain in the Mediterranean when Rome controlled its ports?

Pirates could hide small craft in remote inlets and blend with armed merchant activity, although strong Roman fleets usually curtailed them quickly.

Control of major ports did not eliminate every secluded inlet where a small vessel could be hauled ashore and hidden. Beachable craft allowed raiders to operate outside the infrastructure Rome watched most closely. Some heavily armed merchant crews also shifted opportunistically between trade, anti-piracy work, and predation. At the height of Roman naval strength such activity tended not to last long, because patrol forces could eventually suppress it.