I don't really see the reason to preemptively lock communities in that manner, is there really much harm in letting them exist? I get consolidating communities that are literally clones of each other but none of your examples fall under that for me.

I personally wouldn't lock subs out of only inactivity at all. What if someone tries the Fediverse for the first time, sees that their niche sub exists and is faced with a "SUB LOCKED" message? Is that a better situation than them just seeing a long time having passed since last activity?

People often express this view. And, in practice, it does seem to mostly work that way. But why? There's no reason it should have to. There are many oldschool forum websites where the entire website as a whole has less members than there are subscribers to individual comms on Lemmy. Yet those forums have individual subforums with greater post volume/rate. Why should this be?

I think the problem is that most Lemmings are reddit refugees. They still have reddit-brain. They expect every Lemmy comm to be a constant firehose of content that they can just passively consume, and only occasionally post to. Even though the constant firehose nature of Reddit was largely bot-driven. So when there's no constant stream of content, people incorrectly think the userbase is too small, and check Lemmy less often... which means they post less often, which means there's less content. It's a vicious cycle.

I think people need to come into Lemmy with a healthier mindset. It is a community to participate in, not a feed to be consumed. Lemmy isn't Reddit, and shouldn't try to be.

And that's why it's usually recommended to find a more generalist community where there is at least another active poster.

Keeping a community active by yourself is quite tiring, and most people will drop it after a bit.