You think most new authors have wealthy families?
That is a very odd assumption, given how hard it is to write a book... and given how low the returns are... and given how many other ways there are to achieve prestige... and given how little people regard authorship these days as a measurement of it... and given how unlikely it would be for wealth to have an outsized representation in a career generally associated with poverty... and how all old authors were once new authors which would imply that most of them are wealthy too, which, not so.
It is worth pointing out that there's nothing particular odd if it were the case that writing was subsidized by wealthy families. For the vast majority of the history of writing, writing was subsidized an left to monks, philosophers or aristocrats. It's only been in the relatively recent time period that writing was a potential occupation for anyone interested with enough skills/talent.
so is the only reason for using a traditional publisher is the cash advance then?
The publishers that most writers adore would never profit from white supremacy, yet they are fine with a middleman, no different than airbnb and Uber, that has no publishing standards because self-publishing on a blog or something similar is some antiquated symbol of failure in the modern literary mind.