A new brand would need to start from smaller than scratch? So what? People start new companies every day.
It would require tens of millions of dollars of investment? So what? We keep being told how capital markets are just sloshing with cash looking for investment opportunities; that one of the reasons for rising inequality is due to the dearth of investment opportunities for the rich to use to seek returns.
They'd have trouble finding customers willing to give them a shot? So what? Every startup has this problem. You solve it by differentiating yourself from your incumbent competitor. When your competitor is so hated that they're getting negative press in national news outlets and state legislatures are being pressured to pass laws, your differentiation proposition is practically written for you.
I'm sure there are tractor upstarts out there trying to get funding. The question is, if they're not getting funding then why not, and why doesn't anybody know about them?