I mean, fundamentally, on your own private property you are far less likely to cause injury to someone else or someone else's property, for the sheer fact that people would be trespassing on your private property to be there for the accident to happen. There's a material difference between private and public property, one having more chances for injury of others than the other.

I don't know about DUI specifically, but this is why crimes have many degrees of misdemeanor and felony for the same core behavior.