One reason why the behavior of corporations and other large organizations often seems so irrational from an ordinary person's perspective is that they operate in a legal minefield. Dodging the constant threats of lawsuits and regulatory penalties while still managing to do productive work and turn a profit can require policies that would make no sense at all without these artificially imposed constraints. This frequently comes off as sheer irrationality to common people, who tend to imagine that big businesses operate under a far more laissez-faire regime than they actually do.

Moreover, there is the problem of diseconomies of scale. Ordinary common-sense decision criteria -- such as e.g. looking at your life history as you describe it and concluding that, given these facts, you're likely to be a responsible borrower -- often don't scale beyond individuals and small groups. In a very large organization, decision criteria must instead be bureaucratic and formalized in a way that can be, with reasonable cost, brought under tight control to avoid widespread misbehavior. For this reason, scalable bureaucratic decision-making rules must be clear, simple, and based on strictly defined categories of easily verifiable evidence. They will inevitably end up producing at least some decisions that common-sense prudence would recognize as silly, but that's the cost of scalability.

Also, it should be noted that these two reasons are not independent. Consistent adherence to formalized bureaucratic decision-making procedures is also a powerful defense against predatory plaintiffs and regulators. If a company can produce papers with clearly spelled out rules for micromanaging its business at each level, and these rules are per se consistent with the tangle of regulations that apply to it and don't give any grounds for lawsuits, it's much more likely to get off cheaply than if its employees are given broad latitude for common-sense decision-making.