Freedom
Because freedom is a value in itself, and any restriction of individual freedom has to be balanced against the benefits that other members of society gain from restricting the freedom of the former.
It is against the accepted principals of the 'free world' (albeit regrettably an increasing habit of bureaucrats around the world) to justify draconic restrictions of individual freedom with marginal, incremental benefits to the rest of society. If minimal reductions of third parties's exposure to statistical risk would be enforced at all cost, we all would have to be condemned to stay in bed and not to engage in any activity whatsoever.
The accepted principal is that there always is a trade-off, and generally that there are accepted residual risks of life. In aviation, this is what the ICAO rules (as well as FAR's, or South African CAR's) refer to with avoiding "undue" hazards. It implies that there are "due" risks that are acceptable to society.