Why am I always the one fixing a system I didn't build?

You see the gaps because you are paying attention. That is why the work keeps landing on your desk. No one assigned it to you in writing. It simply became yours, request by request, because you were capable and present. This is not fair. But noting the unfairness will not lighten the load. Separate what is yours to control from what is not. Your effort, your hours, your answer when asked again — these are yours. Whether the organization ever becomes just, whether your colleagues choose to carry their share — these are not yours to force. Stop spending your strength on what you cannot move. The real question is not how to make them stop asking. The real question is what you will now agree to do, and what you will refuse. Decide that today, not in the heat of the next request.