Professional conferences are different because the fear of ending up in a disciplinary hearing at work on Monday morning sometimes (but not always) exercises a restraining influence.

If you pour enough free alcohol down even the stuffiest professionals, eventually this ceases to apply . However, my experience suggests that the window of opportunity between inhibitions dissolving and stomachs requiring pumping exists but is comparatively small.

Fandom is in playtime, so you don't have the same controls. I don't think that fandom is exactly Sodom and Gomorrah, but even a fairly low level of problems is still a problem for organisers.