"The slaughter itself must be done by a sane (mentally competent) adult Muslim."
The immediate reason for live exports now is there there's a premium on live sheep, often in the middle east.
Anyway, either the exporting or importing country can "ban" live shipping, so if origin and destination countries have different opinions that doesn't mean things can't change.
Obviously ban doesn't mean ban, just regulate to the point where transport-to-abatoir doesn't make sense. Obviously breeding stock and such will still travel.
It's actually not particularly difficult to do halal slaughter, the two main requirements are that it is killed with a cut to the throat (common in non-halal slaughter) by a Muslim.
global (aka long-distance) trade started around 3000 BC. it got a boom in 1815 due to mechanisation.
if you want to find out more, this is a good place to start: https://en.wikipedia.org/wiki/Trade
why not? if i sell my sheep and need to deliver them to the buyer, then i'll need a form of transport.