TGT comes in, and the pack from the latest expansion is replaced by a random pack. Another expansion comes in, and we're back to a pack from the latest expansion. Looks like Blizzard always knew that TGT was a failed expansion and no one wanted those packs... :)
Seriously, though, I second/third/whatever the idea of having instead a voucher for a pack of the player's choosing.
I am super happy with the change. With great effort i got a full collection and random packs would make arena less attractive for me and therefore would somehow punishing me for getting a full collection, since i really like playing arena. Knowing that i always get a pack that i need also takes away the pressure of making a good run. Even though i don't need other sets i am also absolutely okay with a second pack instead of gold, since the value you get is pretty high.