And also see the comment from the admin below:
Part of the reason is that this instance already has a certain topic around open source and privacy, but new communities are being created for completely unrelated topics. It also causes extra moderation work to look after these communities. So theres no reason to deal with this when countless other instances welcome new communities.
So the basic deal is that the admins have decided that this instance is "finished" as far as community creation is concerned ... what's here is what this instance is about. You may be able to convince the admins to create a new community if it fits, but it's not a free situation.
I feel like it is more load balancing issues. This is one of the more popular instances, so the admins probably don't want to bear the costs of housing too many communities.
A bunch of people rushing in to make and squat on communities. The Lemmy devs also wanted people to find instances that better match the community, so I imagine it will be permanent.