I'm not a lawyer and wasn't familiar with the bill until it was brought up in this thread. Looking at the text of the bill I'd guess that it's because the bill specifically calls for making risk determination on an individual basis[1] rather than for broad categories. The worry would be that despite the bill calling for banks to make these determinations based on "quantitative, impartial risk-based standards", this would actually give them more leeway to discriminate in a much more targeted way.
[1] §2.10 https://www.congress.gov/bill/119th-congress/senate-bill/401...