Yeah, I was thinking the same: most human-scalable data entry ops, like application review, is farmed out to contractors.

That said, there's no guarantee that the contractor will be assigned your application to review. Assuming there are bribes, it likely would involve multiple people which increases it's chances of being revealed and less likely to actually be happening.

grandparent wasn't referring to ROI of the bribe.

Exactly and the simple reason why, which keeps these basic economics of bribery working so robustly, is the asymmetric measures of value/cost inherent to the two sides of the equation. A government or facebook employee or whomever who has access to some lever worth a great deal will sell access to it for these fairly small sums exactly because the much greater value isn't actually a cost to them. They're leveraging their access to someone elses resources for personal acquisition of a much smaller but to them worthwhile gain. You'd never convince a billionaire to sell you access to something of theirs worth billions by paying them only millions, but, like you said, you can easily convince a senator to give you access to billions in government resources (tax money) for a few million to their personal campaign.