They might be afraid their algorithms would be too easy to manipulate if you knew all of it's factors. Since testing the all of the possible factors would be cost-prohibitive for most, it's not exactly 1:1 with software development
Maybe I used the wrong wording. There may be legitimate reasons for keeping it vague, because designing tamperproof public metrics for credit approval has huge risks involved, or they may be designed so conservatively that a lot actually qualifying people would now be unable to get a loan. I've personally been bitten by the latter despite making nearly six figures.
Similarily I've not really seen any sites which publish how their anti-spam filters work or what the treshold values are either for similar reasons. They're possible to figure out, but cost a lot more.
Maybe a better solution would be to somehow guarantee that they're consistent with their own rules, and regularly audited so that they're also compliant with the current law?
