Old school progression.
There was only one way to go, plain and simple.
It’s actually a technique that Peter Jackson used in the Lord of the Rings to also indicate progression. The characters mostly move left to right on screen as they travel. Back in the old days of Super Mario, the poor Italian plumber could only go right, as with so many other characters back in that day. Eventually left was added in, but if you wanted to feel like you were moving forward, you always went right.