Board Thread:Manga/@comment-27321453-20180108221508/@comment-1327106-20180113003510

It can't be proven that they didn't bring any back. They had likely the opportunity to do so. Ymir was probably already shipped off to Marley by the time the battle in Shiganshina happened since we don't see her captive anywhere and Reiner was carrying her letter, which meant that neither of them expected Historia and Ymir to meet face to face again. For that assumption to be true, Ymir would have left Paradis before the battle, which means a ship was at the island. If Zeke was sending Mike's gear to Marley, he would have sent it at the same time as Ymir.

Remember training to wear those things is hard, people flunk out because they can't even balance while hanging in them. Zeke wouldn't keep any gear on the island for his own use (Reiner and Bert were equipped for the battle, but Zeke wasn't), so there would be no reason not to send it off with Ymir.

As for training soldiers in Marley, I don't see why they would. Maneuvering gear is made to fight Titans, but Marley is fighting humans. Why would you fly around with a couple of swords when your enemy has machine guns and naval ships capable of coastal bombardment? If you look at Marley's war with the Mid-East Allied Forces, maneuvering gear would have been pretty ineffective. Soldiers weren't concerned about mobility so much as protection and not getting shot.