This is a fair point. I think another point about this is how someone is socialized or raised by their parents. It could be that people from higher socioeconomic backgrounds value PhD work more so than others so they are more likely to attempt to do it.
I don't really see the point in making the claim that there is some kind of bias against people from poorer backgrounds. It just inflames things. Maybe people from poorer backgrounds prefer to seek jobs with higher salaries.
> I think another point about this is how someone is socialized or raised by their parents.
Speaking as someone who went through grad school, there is an enormous amount of information that no one will tell you about unless you know to ask. Otherwise, they'll just assume you know. Basic parts of how academia works are not really explained or communicated to new grad students. So people with parents in academia, or with prior experience, can offer their children huge gains by simply explaining how certain processes work or what it actually means to excel as a grad student to prepare for the job hunt. It's not always "do good research", it could also be "make sure you make a relationship with so-and-so". Asymmetrical information can be a powerful explainer and tool.
I don't really see the point in making the claim that there is some kind of bias against people from poorer backgrounds. It just inflames things. Maybe people from poorer backgrounds prefer to seek jobs with higher salaries.