Owner never applied or wasn't eligible for it?
ETA: Some states require you to apply for the homestead exemption. It is not automatic. And I think you always have to have it be your primary residence. So if the owner wasn't using the house as their primary residence, it wouldn't have the homestead exemption attached. If you buy the place and use it as your primary residence, you'd be able to apply for the exemption. Assuming it doesn't have it already, perhaps that affects your property taxes until you are able to apply for it? I don't know how that aspect works.