People do get promoted and paid for simplifying and refactoring code. Heck, I got promoted and am currently being paid to do just that. It often involves adding value in other ways simultaneously, but what you said is just false.
If engineers want the business to pay them for simplifying maintenance, they can identify a collection of support tickets that have a compelling root cause, and propose refactoring that system to eliminate the bugs and maintenance issues.
What I usually see is us engineers calling it “tech debt” and complaining we never take time for it, which is about as effective as the bookkeeper complaining about the paperwork that debt payments create for him. Businesses love debt. It’s a useful financial tool. The business doesn’t get the issue.