[scotty79]

Why wouldn't they be able to reach us if they started traveling in our direction before the event of the Big Bang?

Even though the spacetime expands if they started their journey early enough they might have been arbitrarily close to us at the moment spacetime within our observable universe started expanding.

For example the front of some gravitational wave originating from outside could be near the times of Big Bang as close to us as the matter that eventually formed Andromeda galaxy. As waves travel with the speed of light it would passed us very long time ago.

The limitations you speak of are calculated with assumtion that both all the matter in the whole universe and the spacetime itself started at the moment of Big Bang.

If there was matter outside our bubble of observable universe and time before the Big Bang those limitations are not valid for anything originating there.