Major reason is sun and stars are represented through these temples which are then the vitality of population. Thats the base philosophy of all these major religion and when mixed produces one God/people/ etc. But it also hides in it a treasure trove of geometric pattern which can be used to illuminate world history. this is the same reason for architecture of other religious traditions. They are all mixed. In the end as I have hypothesized only 20% of world population can be Hindu if there is enough mixing for 1000s of year. (Its possible in as long as it is, I mean there has to be sufficient mixing, which being perhaps bellian curve approaches a quick time say 500 years, we have 7K years.)
The vaishya eg is busi-sha = business person, hurriedly made into vaishya. The actual varna could also be (due to racial/religious mixing) Hindu-Jew-Christian-Islam. Which are all considered to be Arjya splitting into Hindu-Jew and then their mixing splitting into Christ and Islam. Also see that this way Mount Moriah might be Mount Meru, the latter is considered to be Hindu-center-of-universe.
This way the caste system is far more understood since, for 1000s of years these major religions were present world wide and mixed up. The other major religion is Budhism. B-ism was also mixed to each of them over time line of history. Which is why Morriah=mo-arya=maha-arya etc which also mean ordain of the God because raya is ordain or ruling.
But this might have been considered in various forms. eg in some places it might have been considered merged with the major religion say (of the) Hindu, Jew or Christ .
That means depending on time line of history, there were different layers, sometimes Brahman-Xatriya-..-Xudra=small/low) sometimes other variants of Jew-Christ-Islam-Hindu mixing and assimilated into different classes/divisions. Expansion/proselytization/conversion/re-conversion/assimilation they all occurred synonymous with religious harmony.
The idea is to give the idea. And Kaku might not have done a fabulous job here. But in the past the debate was blown overhead. I mean there simply is no fault with Leon Lederman. He is an immensity of science and not of religion. Lets not give him less credence than a Templeton quack or a Fundamental science prize winner. Scientists are from scientific passion and not from money or God passion. But there is coincidence. Weinberg had said “Every scientist faces difficulties with language” . Language is theological. Tuft Gerald had said “Language is a social construction”. And The Scientist always faces difficulty from what society is. Its not his fault what society is like. He still has to make a living. But to exploit such conditions is stealing. And I think Kaku over spoke but not trying to steal anything here. Lets keep the community sane.
Hence in akira 智 [which as you see heaven+mouth+energy/sun hence higher consciousness] you have a “Budha” and any child of Budha is Budha. We are all Budha. What a brilliant thinking man made 1500 years ago, but it essentially stole from a religion now called Hinduism and they in turn stole it from the Vedic nomads and the Vedic nomads stole it from a minority who achieved “intellectual understanding of nature’s elements” hence Science. Science is often manipulated into religion and then forgotten in due time.
azuma > asuma > asuna > isuna [of isu, of God, light, sun, fire, existence, rightfullness, person] this isuna is then isana. So what east in Japan is north-east in India if that has to be firmly used say 1500 years ago with their phonetic variations over this time not-with-standing.