We Know that there is great variety among Christians. We are beginning to discover the variety in Islam. Buddhism also has its variety. We as humans, for all our similarities, are each unique. Should we be surprised that we see our religions from so many different points of view?
Theravada is an important branch of Buddhism. I think that it is the dominant for of Buddhism in South East Asia. I believe that Burma, Myanmar, was the principle SEA power in the spread of Theravada Buddhism there. The Sinhalese of Sri Lanka have long been Theravada Buddhists and there has long been a cross-fertilization of Buddhism between what we came to call Ceylon and what we came to call Burma.
In Myanmar and in Sri Lanka Theravada is not the only Buddhism just as Buddhism is not he only religion.
There have been all kinds of Buddhist renewals just as there have been in Christianity. At times much of that renewal was carried by one man. Atisa (AD 982 - AD 1054) seems to have been such a man after the advent of Islam. Atisa probably spent a dozen years in what became southern Burma before going to Tibet to reform the tantric tradition there.
Theravada stayed strong through the Mongol invasions and the destruction of Pagan by them at the end of the 13th century. In the 15th century the Mon Dhammaceti order restored Theravada again.
You might find it interesting to check out Atisa and Pagan on line in Wikipedia or elsewhere. You might even find it fun to review the basic tenants of Buddhism.
