Sometimes you want to start where the belt/train line should end up, not where it starts.
In satisfactory when you are at a machine/platforms input location, and you start a belt from it, it is smart enough to know the direction you want.
With platforms here it always assumes you want to start the belt/line there, not finish it there.

This was possible in Shapez 1. There we could just push the Alt key and it would reverse the direction of the belts.

I was thinking you could do that sometime along the start but IDK if you still can … it is very useful to just be able to hit a key to swap the direction after the drag