Why Rama born as a normal human being?

Rama was born as a 8th incarnation of lord Vishnu from the Raghukul of Ayodhya. The main aim of Rama was to kill the most cruel king of that time, Ravana. Ravana had a blessed not to kill by god, demons etc which was given by Lord Bramha. But Ravana didn't say human and monkey while begging a blessing.

So to fulfill the destiny with recreation of dharma, lord Vishnu incarnated his 7th birth as a normal human being and eventually killed the Ravana at the end.