Camp fires can get too hot and oxidise the outside of the pan, ruining it. It turns pinkish and won’t hold seasoning more. You need to get them _really_ hot for this, but it’s not like you can know or control the heat a campfire is putting out… (Source: many damaged pans on r/castiron)

That's fair. I'm a hobby soapmaker so I've done the "bucket of lye water" method before without much fuss or worry, but that wasn't being asked about.