FTL, ether and wind

Just why would FTL lead to time travel?

Because the simultaneity is relative, for the slower than light
communications?

But why should inertial frames be equivalent when it comes to FTL?

If you can send a ****p or a message from point A to point B and back
in zero roundtrip time, you can compare the real simultaneity of
events as established by FTL with the outcome of lightspeed signals
sent through ordinary space. This would enable observation of ether
wind - inertial frames would no longer be equivalent. Only in FTL,
though - all predictions of relativity as to STL effects would still
hold.

Also, what happens if Earth turns out to be subject to strong, indeed
relativistic ether wind?

For example, because Earth turns out to be some distance away from the
epicentre of Big Bang?

Is it possible to come up with a noncontradictory metrics where ether
itself expands?