Why is it we tend to come down hardest on the people that do the most to help us, the people that will rather than the people that should?
Just because they always do what you ask of them, you expect more. The workload becomes increasingly imbalanced. Those who do, do more. Those who don’t, avoid the work and the weight of expectations.
It’s hard to break the habit. It requires more of us too; to distribute the work evenly, to battle against the inertia. Things will take longer, need to be checked more thoroughly, require more re-work,
The alternative of course is to recognise the work that is done. Reward people disproportionately. Make it worth their while. If some people are special, make them feel that way. Make the others envy them, strive to emulate them, then give them a chance to grow. Make it right!