I think the reason feature flags are never removed is because the timeframe that a given feature-flag is top-of-mind is also when it's at its most useful. Later when it's calcified in place and the off-state may be broken/atrophied, no one is really thinking about it.
I'm also not convinced it's always a huge problem. I can imagine sometimes it is, but in most codebases I've worked on, it's more of an annoyance but not cracking the top 3 or 5 biggest problems we wanted to focus on.
IMHO the best solution is not something heavy handed like a policy that we only use run-time config for fixed timeframes, or a process where we regularly audit and prune old flags. It's simply to keep a record of the config changes over time so anyone interested can see the history, and a culture where every engineer is encouraged to take a little extra time to verify and remove dead stuff whenever it crosses their path .
The mental overhead of reading code like this is massive. Leaving feature flags in with the alternate branch left to rot leads to a codebase that is nearly impossible to understand. No purpose is served by not deleting the now unused branch except you save one developer an afternoon of work. But that time is quickly recouped when the entire team, and especially new hires, only have half as much code to understand.
I'm also not convinced it's always a huge problem. I can imagine sometimes it is, but in most codebases I've worked on, it's more of an annoyance but not cracking the top 3 or 5 biggest problems we wanted to focus on.
IMHO the best solution is not something heavy handed like a policy that we only use run-time config for fixed timeframes, or a process where we regularly audit and prune old flags. It's simply to keep a record of the config changes over time so anyone interested can see the history, and a culture where every engineer is encouraged to take a little extra time to verify and remove dead stuff whenever it crosses their path .