They didn't have any ship. That's why they are discussing how to bring the children to holyland because they can't pass the gate without the mark and they don't have any ships.
What if Harald recieved the mark to pass the gate
@soupongo ? That still leaves the question why the WG didn't use the gate before until now and why now, even if Shanks was protecting Elbaph it's the same shit now Luffy is in Elbaph so the same shit.