Buddha was born in Bharata when there was a decline in Dharma. Termed as dark age of India.
As Gita says.....
Whenever virtue subsides and wickedness prevails, "I" manifest Myself. To establish virtue, to destroy evil, to save the good "I" come from Yuga (age) to Yuga."
Buddha reformed the Dharma again, this happens around 2400 years ago and he was the last Prophet born in India.
In ancient times writing materials were not easily available, and it may have been customary in those days not to write down the teachings of the Buddha. So the teacher taught, and the students learned by list