There's lots of 'normal' quests that Destiny has that forces people into PvP, such as the sword quest and many of the old exotic bounties. Not everyone is 'good' or can 'get gud' (as so many 'experts' like to say) at PvP as they have no desire to do so, so they do the simplest thing to get it done and over with the quickest, which is usually to hop in a Rumble match with friends and just kill each other until that part of the quest is complete. The only ones that can really be blamed for it are Bungie for forcing people to do PvP, the same as some low-level people can have trouble doing patrols and stuff because of all the high level people forced to do their missions and bounties in the shared PvE areas.

Ah ok lol