You have automated tools that yell at you to clean up feature flags and you force people to include sensible expiration dates at part of your PR process. Flags

You have automated tools that yell at you to clean up feature flags and you force people to include sensible expiration dates at part of your PR process. Flags past the date result in increased yelling. If your team has too much crap in the codebase eventually someone politely tells you to clean it up. You also have tooling that measures how many times a flag was encountered vs. how many times it actually triggered etc. Once it looks like it's at 100% of traffic, again you have automations that tell people to clean up their crap.