I went to a thing. I'm not going to name and shame, but I didn't like it and I didn't stay.
It failed the "3 Hellos" test. I said hello to three people and each of them said hi back but nothing more, and went back to what they were doing. These were all people who were wearing t-shirts proclaiming themselves to be part of the thing.
Nobody asked if it was my first time, nobody else offered an unsolicited hello. I tried to follow on with one person "so what are you doing?" and they came back with a closed answer. Nothing actively hostile, just not actively welcoming either.
Now, it's OK - some people don't have great social skills and what makes them good people to have at a thing like this, might not be that they know how to talk to people. But I can't run something like that now without making sure that there's at least on someone tasked with greeting and welcoming. Saying hello first! And letting people know that they're in the right place, maybe finding out what's important to them and trying to help them find it.
It's such a natural part of hosting to me that I find it surprising initially when it obviously isn't happening.
But hey! They're nerds! What ya gonna do?
Trouble is, it gives self-organising a bad name. It's this sort of thing that encourages the Organisers to put artificial shit in to "break the ice" - it can happen organically, without too much organisation but someone has to pay attention to it. It's one of those things that fits into "as little structure as is needed to make something happen, and no more"