The bacon cheeseburger is not a cheeseburger with bacon added on a whim: the bacon is a structural decision about texture. A beef patty with melted cheese is soft on soft, the only firm element being the seared crust on the meat, and the bun and the cheese both yield. A layer of crisp bacon laid under the bun lid introduces the one hard, brittle, salty element the build otherwise lacks, so the sandwich reads as a sequence of textures rather than a single soft note. That snap is the whole reason the bacon earns its own name on the menu.
The craft is in how the bacon is cooked and where it sits. It has to be rendered crisp and kept flat, because a limp or rippled strip slides on the cheese and the structure shears apart on the bite. The placement is deliberate: bacon goes on top of the molten cheese, not under the patty, so the cheese glues it down and the strip stays put while the burger is lifted. The patty is still the fixed point, seared hard on a flat-top with the cheese added while the meat is on the heat so it melts into the crust and partially seals the patty against its own juice. The bun is soft and sized to the meat so it compresses rather than fights, and the pickle and raw onion remain the cool, acidic counter that keeps a now richer, saltier build from collapsing into one heavy register.
The variations are a matter of how far the richness is pushed and on which burger base. The double bacon stacks two patties and doubles the cheese; the smashed bacon build presses thin patties for maximum crust under the bacon; barbecue-and-cheddar and onion-ring versions lean further into sweet and char. Each of those keeps the founding rule and changes one element, which is the same impulse that pulled the bacon cheeseburger out of the cheeseburger in the first place, and each deserves its own article rather than being crowded in here.