I assumed it was because of an issue having to do with fire hazards. If you have equipment with you and around when you're at a con, it can block a hallway and even in general can cause someone to trip over the equipment.
Staff are probably just annoyed because they have to deal with a lot of things and seeing people with a lot of or expensive equipment means paths will be blocked or there is a potential of the equipment being stolen, and people falling because of it.
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