I made a scenario that's 30 miles in length and the switcher is facing backwards and not forward during it. I don't understand why I have to travel in reverse on the main line.
They travelled either way just as easily and at the same speed - if by backwards you mean with the cab at the coupled end, it did happen often on trip workings as there's nowhere to turn them in real life.
Besides, your visibility is way better from the blunt end than looking down the side of the nose. With the Class 20, BR eventually just decided the cab end was the "front."
The class 20 almost always drives "nose to nose" so you're essentially always driving backwards. In reality they drive the same backwards or forwards but for visibility sake anything with a long nose (such as 08/09) tends to drive blunt end first.
A similar evolution happened with US diesels, and for much the same reason: steam engines always had the cab at the back looking down a long nose, so early diesel switchers and road switchers were built to the same configuration. But after a while RR started ordering GP7s with control stands facing the other way (or in Norfolk & Western's case, both ways).