This is what we’re looking for! Mortgage lenders are much less likely to take the time to comprehensively evaluate borrowers with the highest credit scores, so they end up loaning to riskier people whose red flags would have disqualified them if the lender had looked closer.

This doesn’t describe any difference between the highest-credit-score borrowers and the others. Because these inaccuracies presumably occur across the board, (B) doesn’t explain why a correlation that holds for most borrowers falls apart for those with the highest credit scores.

Of course this is true! These factors play a huge role in a person’s credit score. But that’s true for every person at every credit score level, so nothing here explains why a correlation that holds for most borrowers falls apart for those with the highest credit scores.

Of course this is true! Houses are expensive. But this doesn’t point to a difference between highest-credit-score consumers and others, so nothing here explains why a correlation that holds for most borrowers falls apart for those with the highest credit scores.

This seems quite plausible, but it doesn’t help us understand what’s happening for mortgage borrowers with the highest credit scores that’s different from what’s happening for other borrowers.