Noone does the events in VB, because we don't need to defend camps. Most people are coming to VB only for Wyvern Matriarch and Amalgamated Gemstone. All you have to do is get on the platform with your griffon and just wait for boss. Not everybody can get there, because there are people that don't have griffons. Primary rally point is often fallen, so sometimes VB meta seems to be only for people with mounts.
I think reward should be granted after killing all bosses or reaching participation threshold or after the night. Same in AB. You don't have to participate in meta event. You can come after the event and just loot all chests. Maybe reward chest in AB should be granted for killing an octovine?
Rewards from TD and DS requires completing the events. Why not in AB and VB?
In PoF maps: Junundu can be looted without participation.
Forged With Fire and Serpent's Ire needs to be completed.
Maw require defeating the Legendary Demolisher.
Piniata: You have to destroy the piniata.
Doppelganger: Boss needs to be defeated.
Commander, to ME!