If by “well maintained” you mean keeping a whitelist of instances, then yeah. But I doubt anyone is doing that because it’s actually counterproductive to the concept of fediverse. By keeping a whitelist you are creating an in group and an out group and instances can live or die based on that grouping.
As for why you’d need a whitelist, you can’t defend against a malicious attack if they keep spinning up new instances with bots designed to spread misinformation. The moment you ban once instance another one gets spun up. The only solution is a whitelist so all new instances are automatically blocked. Of course that works if all “normal” instances also have proper registration policies and can’t become attack vectors.
If the fediverse becomes wildly popular defending the instance can become a full-time job as the open nature gives more attack vectors. Also most instances are ran by volunteers so it’s probably not going to be a good time for anyone.