Pilots can't get ahead by cutting corners, and (to a somewhat lesser extent) it's hard for maintenance people to be pressurised to sign off on unsafe work.
Indeed, but also no incentive for bypassing safety checks that are redundant most of the time (which is how you get the normalisation of deviance that eventually leads to catastrophe). Sometimes that's the right tradeoff.
All metrics are gameable. I think I once saw a study that suggested that every metric applied to professionals ended up having a net negative effect on actual productivity - by and large people understand their job and want to do it well, and while a metric may incentivise the few that don't, it also ends up distracting the majority.