npc celebrities losing fame

in all my saves, no matter if sims start opted in or out of fame, townie celebs (brytani cho, judith ward, etc) experience fame decay until they're no longer famous. i have no mods or cc, and neighbourhood stories are off if that makes a difference. any ideas on how to stop that? even with cheats it doesn't seem like i'm able to freeze other sims' fame unless i play them.