It’s the rancour caused by such a modest-sized community with no real intake and no prospect of that changing. Under a permamod system, hostility will fester between the mods and some minority of posters, because humans are flawed and bias is inevitable.
So you might say: Well, mods now have to seek re-confirmation. But here we encounter the fact that most people simply don’t care that much. Most people are just going to want to not have to think about it and, if neither they themselves nor a poster they’re especially tight with have beef with the mod, they’re mostly just going to re-appoint the mod. I think this leads to what you might call the tyranny of the indifference of the majority. And I’ll again stress that none of this requires any malicious actions or intentions on the part of the mods.
But if there are term limits for mods, that avoids the re-appointment by default that leads, in my view, to permanent alienation of some minority of posters who may not ultimately be deserving of that.