Simple, it looks weird if the front is level with, or lower than the rear.
I also like to have a slight bit of tilt toward the beater. I feel that the drum plays better that way.
I make sure to always avoid putting stress on the hoop where the pedal clamps onto it.
If you are using a newer model dw pedal that is a non issue because of the floating clamp design.
I used the, "level" app on my iPhone to measure tilt. All 4 of my bass drums on the kits that readily had set up were about 1.2 to 1.4 degrees tilted higher in the front.
I was surprised at how consistent they are because I always just set them by eye.
I was never taught to set the front slightly higher, it was just something that I have always done. I have a mechanical mind and I often trust my instincts when making such judgements even though there is no exact science to me reasoning. I think that my inner zen is thus; When the beater strikes the bass drum it will be deflected down slightly because the beater is set a few inches higher than center on the head.