I suppose, to help a simpleton understand relativity better. If the earth is in motion in a specific direction, then we would have different maximum velocity depending upon whether we launched with or against the earth’s direction of travel.
I have heard this before many times, ‘we can’t reach some parts of our universe because of expansion’ but can we launch a massive rocket and then launch a rocket from the first rocket in the same direction and then again and again? Due to relativity.