Why did the GM do this?

Its a real question, not a QQ. (TL;DR version: Why can GMs reimburse certain items only?)

Last night I was looking for someone to do an enchant (Power Torrent) for me. Someone messaged me, said they could do it. I said ok - hang on, and I got onto my alt to grab my mats out of my alt bank. I logged back on, invited the person who said they could do it, and traded: 4 Maelstrom, 8 Heavenly shard and 20 dusts. They took the items, ran from me to a mailbox, stood there for a minute, then logged off.

They came back about 10 minutes later, ran in circles around me (and only me), flew into the air, and shouted about free gold from some website, and logged.

Came back 10 minutes later, said in trade, "Lol, whos hackin me?" so I sent him a whisper telling him (not so nicely) to give my materials back - NOW. He put me on ignore, and then proceeded to run away from me every time I found him.

I made a GM ticket about this reporting his theft right away. I just got a reply now (about 12 hours later) saying that action was taken (didnt say what) but they also said they could not recover my items to me.

Why? The items werent deleted, they were just sent somewhere to someone who didnt earn them. When my gear was deleted when a hacker got my toon (when I was inactive last year) everything, even my gold, was all reimbursed. They were SOLD! They no longer existed on my toon. So, why is a gm unable to restore items that most likely still exist, with proof of logs showing that they stole it from me?

The person in question I later found out doesnt even have enchanting as a skill.. ugh.

So again, not a rant or qq, or a gimme my stuff back, but I honestly truely want to know why a GM cannot reimburse something stolen from me, that another person will profit off of (over 1000g) after their temporary ban is over. *boggled*