Because of its simple truth, the Golden Rule (Do Not Do Unto Others What You Wouldn’t Want Done Unto You), rules.
It’s older than all religions; not unique to any; is not unique amongst humans alone; it does not require the selective self-categorisation of the scriptures you call your own into myth, allegory, mumbo-jumbo, truth / half-truth, metaphor and what-nots; it can fish out the moral choice from a wild array of circumstances; and is the basis upon which social cooperation and amity rests.
It’s a single, simple rule that replaces any scripture with their wild contradictions that are conveniently ignored, and hence, is superior.
Ok, it's simple, it's old, it's not unique, it replaces scripture, it ain't myth or allegory or metaphor… All these things you like about it.
Because of its simple truth
Why is it true?