It might not seem fair when you first look at it, but it is fair that if someone’s lot is damaged due to a defect in common property or something that is OC responsibility, then the OC has the responsibility of fixing it.
The only reason that certain owners have to have their bathrooms repaired/renovated is because of something for which the OC is responsible. In the case of owners who aren’t affected, they have a choice as to whether they renovate or not. The owners with damaged lots don’t have that choice.
You can draw an analogy with insurance. You pay insurance to cover you for the possibility of having to make a claim on it, but you may never have to. Your premiums are paying for the people who do make claims. Obviously that is not quite the same situation, but the other thing is that when you buy into strata you accept that you are responsible for things like this.
It’s not quite clear whether the movement you refer to is something like an earthquake or a natural occurrence, in which case as kiwipaul suggests you should check your insurance policy.