I love the campfires, I think they were a great addition to the game! But, I really wish they worked in dungeons. I cannot speak for raids, but that would be cool too.
Perhaps this just comes from reading LitRPG books and other fantasy type novels. I truly believe this could add to Immersion in game especially on the RP side of things. Crawling through a long dungeon, people need to take a break. Why not set a camp up with some bonuses, and while the group waits for others to return they chat, maybe share stories or create a really fun RP moment. Maybe they just want to camp FOR that RP moment.
There is no reason not to other than taking the time to code it in (yes easier said than done) as people set camps outside dungeons quite often.
Maybe I am off base with this. I just think it would be really fun for a lot of scenarios.