@Zasz_Zerg Really? I know I've done it. Are you sure you're using the Outdoor Retreat campfire and not the Get Together bonfire? The OR campfire has more options.
[edited to add] Okay, I just tried it. You need the Outdoor Retreat campfires. There are a couple of almost identical-looking-in-BuildBuy items that are much larger from Get Together (bonfires) that offer, alas, squat in the way of cooking. However, both the campfire options from Outdoor Retreat do let you roast things. (Fish and beetles are grayed out because she doesn't have either.)
My camping-obsessed Sim loves to roast fish over campfires in Granite Falls, and roasting beetles is required for the Outdoor Enthusiast aspiration so I've done it (ew).
[Edited again to add, since I kept thinking...]
Aha. Ahahahaha. Ahahahahahahahahaha.
It's the Simple Living lot trait.
With Simple Living:

Without Simple Living:

I'm going to go open a bug report now... Click "Me, too" here. https://answers.ea.com/t5/Bug-Reports/Can-t-cook-on-campfire-when-simple-living-applied/m-p/10579177#M195362