Some real examples that are specific to the trip I take:

There is no rail service that goes there. It would be a combo of trains and busses that takes significantly longer and costs more than the gas.

Our dog comes with us, generally isn't allowed on mass transit, and the much longer trip would stress her out if she was.

There is little to no mass transit in the town they live in to get around once we arrive so we'd end up borrowing or renting a car anyway.

With limited amounts of time off, making the trip overnight adds a full day of getting to see our family to the trip.

The only other realistic means of getting there is flying but, I enjoy driving and hate everything about air travel. It's a pretty cheap flight for one person but becomes more expensive once you add in the rest of the family and the dog can't come.

Edit: formatting