The bottom of my oven is like a montage of dinners gone by.
Here are my reasons for not cleaning it:
1. I'm nostalgic about food
2. I don't think it is safe to use oven cleaner when there's a toddler in residence
3. Preheating serves as a tidy way of testing the smoke detector
4. If you season a cast iron skillet why not also season your oven?
5. It's bbq season anyhow