Why was Buddhism attractive to lower castes as an alternative to Hinduism?

Buddhism was promoted as an alternative religion to
Hinduism by Dr. B.R.Ambedkar, a senior politician and statesman of India, in some kind
of protest against the discriminatory treatment received to the Hindus from the lowest
caste, who were considered untouchables by Hindus of the upper caste. Thus it appears to
be an attempt on part of Dr. Ambedkar to give greater social acceptability to the
Hindu's of lower caste. It was perhaps also a a political move on part of Dr.
Ambedkar.

Dr. Ambedkar, a Hindu from a lower cast, turned
his attention to Buddhism in 1950's. In a public meeting on October 14, 1956 he formally
converted to Buddhism, and then proceeded to convert an estimated 38,000 to 50,000 of
his supporters gathered there.