I won't parrot the reasons, I think other comments captured that.
However, I would MUCH rather share links in professional circles to something called programming.dev that is specifically an instance about programming rather than "choose your random generic instance" that has porn, memes, shit posts, etc. and oh look, a programming community too.
A lot of the time I don't even know where a post is coming from. They show up on my mastodon feed, I reply. I've clicked source links before and gone to completely new lemmy instances I never knew about.
I presume, since this whole instance is programming specifically, it makes sense to have programming communities here, even if other instances have their own.
Because we can. Because that's how federation works. If you don't like this instance, go to another. Or make meaningful strides to make this one what you would like.
Beehaw already defederated from Lemmy.world, so I can't even see it. It's just a preference and if there is no activy at any given instance... Then that's fine. Maybe each find its own community preferences and rules. Maybe you just participate in both like many people are.
If we had a large user base, I would totally see the value, but right now lemmy is still relatively small. Don't you think new content will be too slow? Especially the rust community with around 300 subs for each one.
As I see it perfect is the enemy of the good in this case. Rules, official or unofficial, on the "correct way" to do things stifle growth especially when there's few contributing users. That little extra barrier is enough to keep many people from even bothering at all. You want people to be engaged and excited rather than feeling they're beholden to a bureaucracy. Or worse beholden to an existing group of power users that control things by being the first or the loudest.
That's just the way things work when humans self-organize. There is the appearance of structure at the beginning, because there just aren't that many people with shared interests. Then as people are unsuccessful in finding the community they'd like (assuming they even looked!) more are created. Then more people come in and mill about and browse and get overwhelmed by the search for a needle in a haystack, so they create more.
Eventually, some communities reach a critical mass and a bunch of small ones fade away into near irrelevance or disappear completely.
As far as I know, the only way to put the brakes on community over-proliferation (if that's even a real thing!) is to add a bit of friction to the creation process. Many kinds of friction devolve into centralization and gatekeeping, so they tend to be avoided in projects like this.
The only kind of friction that I can see working and gaining acceptance would be some kind of "have you tried these communities?" auto-search during the creation process. Simply asking people to search first is unproductive for two reasons. First, people are notoriously bad at imagining that someone else might have thought of something first, especially when they are only person they know with that particular interest. (I've only met a dozen other programmers in 43 years. In my entire life (66) I've not met a single person with even a passing interest in boatbuilding, let alone an actual boatbuilder, etc). Second, even if they consider that someone else thought of it first, people are notoriously bad at searching.
One of those, I am not allowed to participate in or look at due to my instance being sh.itjust.works. Behaw defederated, and thus I am not welcome in these communities. These new communities have not defederated and thus are the ones I'll be participating in.
If we're not welcome, why not create another where we are?
That is their statement, but this doesn't change the outcome. I cannot participate, I am not welcome in their communities. I see no reason why new communities can't be created on instances which won't defederate, even temporarally.
When it comes back, I'll still avoid the instance. I'm not going to participate where I could suddenly become unwelcome again. They've done it once, they'll do it again. As is their right, the heavy handed moderation is their stated goal, but it's also my, and other peoples, right to simply go elsewhere when we are unwelcome.
Other instances will do this too. One answer to this question of 'why create another copy community' is for this situation. When we are no longer wanted in one place, why not create another?
Thank you for the kind reply though. While I disagree with the action I'm happy they have the ability to create the site they want
For future reference I think this post would be a good candidate for Programming Meta community we have here. (Not saying you did something wrong, just sharing that it exists 👍.)
Because we're in a period of rapid user migration and not everyone is aware of what communities already exist, or have a different idea about how they should be structured. After a couple months of people shifting between servers everyone will get settled and we'll see which communities will survive vs which ones will be determined to be redundant.
I'm over on programming.dev (https://programming.dev/communities) -- I really like the idea of servers and thus the sub /c's being centered around topics of interest. I think there's going to be a lot of "generic" lemmy servers still, but I sort of liked how "places" sort of picked lemmy.world, for example (though that's starting to fade with lemmy.world becoming more popular).