They're just pinned. You can help LSCM to unwrap the way you want by using pinning. Also if you want to unwrap just some of the islands again then you can pin one vertex per island you want to keep the way they are.
Just a technical quibble. Don't put a vertice in the middle of your barrels. If the area is going to be flat anyway, you can cap it off with two fewer polygons by removing that vertex. The changes you made to the barrels also make them look less round than they probably could be. I'd stick with the basic circle shape for…