First off, that failure wasn't supposed to happen - the nacelle should not fail due to a FBO (reportedly Boeing had a fix in the works for the nacelle coming apart - which apparently was delayed because of the FAA paperwork - which should have prevented the nacelle failure in the similar UAL event in Denver).
But more to the point - FBO is a rare event - something like 10-7 per flight (which, BTW, is the same probability number used for an uncontained rotor burst failure). And FBO at cruise is extremely rare - nearly all FBO events are during TO or initial climb. So you're talking an event probability that is way out there - the same sort of probability that an uncontained engine failure will cause catastrophic damage. Yes, it happened - but so do many improbable failures that endanger continued safe flight and landing. The statistics are solid - adding engines doesn't improve safety. Quite simply there are better places to spend money if the goal is to improve flight safety.