Because it's not always used for monitoring the main battery in a car. If you have a caravan, camper trailer, boat, etc with a battery in them then you often w

Because it's not always used for monitoring the main battery in a car. If you have a caravan, camper trailer, boat, etc with a battery in them then you often want to know what the charge is, but they don't have OBD2. Why would a caravan, etc have a battery you ask? Inverters, lighting, fridges, USB chargers.. Lots of reasons.