What prompted Rama to build a bridge to Lanka when he, pretty well, knew about the capabilities of most Vanaras to fly long distances?

What prompted Rama to build a bridge to Lanka when he, pretty well, knew about the capabilities of most Vanaras to fly long distances? When Ravana abducted mata sita and held her into Ashok vatika of sri Lanka. Then Lord Rama with his huge vanara army reached ocean which connects india to srilanka. In Ramayana, the distance between Ravan’s Lanka to India main land was 100 yojanas (approx. 1213 km or 753.52 miles). The most powerful warriors in the Rama’s army was Hanuman who crossed the ocean when jamvanta remind him power . Jamvanta was not sure that he could cross the ocean or not because he was too old for this work. If he was youth then he could do that. Angada the son of Bali who could cross the ocean but he had fear of Ravana’s son Akshay Kumar. Rama requested and prayed god ocean to give a way so that he and his army could cross the ocean but god ocean didn't give any answer. Then lord Rama decided to dry out the ocean. When lord Rama invoked his weapon to dry out ocean then god ocean appeared and said if you dry out me then whole creatures in me would die. Ocean god suggested a way by which Rama with his army could cross the ocean that Nala and Nil two vanara in Rama’s army who would throw strone in ocean then stone would float due to curse. Lord Rama did as the ocean god said and made the stone bridge across the ocean.