Oil isn’t so much more expensive, it’s just a big hit every time they come fill the tank. Instead of having a steady monthly bill, you get basically no cost all summer and fall, then a few 600 dollar bills in the winters, then nothing again. If you have some flex in your income it doesn’t matter, you end up spending the same amount of money on heat. For some folks it’s a little easier to have monthly payments that never go above a couple hundred bucks even if annually it’s the same amount paid.