Importance of Oil Bath (on Deepavali and Other Auspicious Days)

Why do the Hindus give more importance to the Bhagavad Gita than to Uttara Gita?
 

Swami Sivananda, "The Bhagavad Gita is more comprehensive and detailed in the exposition of the philosophy and teachings of Sri Krishna. Rather, it is a magnum opus among the scriptures of the Hindus, and so, in substance and scope, it is more important than the Uttara Gita, also of Sri Krishna. But please note that there are many Gitas, such as Anu Gita, Avadhuta Gita and so on, all of which are helpful to the spiritual aspirant. Yet, among all Gitas— quite a few dozens of them, major and minor, the Bhagavad Gita is the most important, integral, comprehensive and the best."

(pg. 204, May I Answer That?)