Policies like that are often designed to (or at least conceived/fantasized to) ferret out/prevent single-actor fraud.
Forcing someone to take two contiguous weeks out of the office means that someone else will need to be briefed for continuity and there's an enhanced chance of detecting "weirdness" that might be associated with a fraudulent scheme.
Yes, 'conspiracies' of more than one person are much harder to keep under wraps. That regulation was directly in response to the high-profile cases of rogue traders.