Before LiPo, wires were commonly soldered directly to the battery, no connector at all. When LiPo was introduced, I believe rules were put in place that a connector must be used with LiPo for safety reasons, as LiPos are much more volatile than the NiCd/NiMH they replaced. You'd have to ask the manufacturers why they chose to standardise on bullets, but they actually work fairly well. You keep saying that the only time you'd use bullets are on multimeters, but they use different types of bullets. In the attached image, the left bullets are the cheaper ones used in many devices, the right ones are typically used for higher performance RC applications.