It is a standard idea in stochastic explanation that factors that affect the probability of the explanandum enter into the explanation even when they lower that probability. While there are indeed cases where probability-lowering factors form an explanation (a standard case in the literature is that hitman A shoots at the victim can decrease the probability of the victim's death, even though the victim dies from the shot, because we can have cases where had A not shot at the victim, a more accurate hitman, B, would have shot at the victim, and the victim would have been even more likely to die), those cases are the exception rather than the norm.
If a building survives an earthquake, we might cite in our explanation of the building's survival the fact that the building had a resilient steel frame, but the fact that the earthquake was exceptionally strong would not be a part of the explanation. At most we would cite the exceptional strength of the earthquake in a "despite" clause:
The building did not collapse because of the innovative steel frame, despite the exceptional strength of the earthquake.But the "despite" clause is not part of the explanans. Perhaps it qualiﬁes the explanandum, the question being why the building did not collapse despite an exceptionally strong earthquake. (This paragraph adapted from my "Plans and their accomplishment: A new version of the Principle of Double Effect", Philosophical Studies, forthcoming.)