The taxman ensuring they still get their cut… 
On one hand, as someone who is not a hardcore Auction House player, I think they needed to rein in the cancelling style of play so someone could:
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experience the nice feeling of selling an occasional item once in a while.
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Afford to buy items needed to access content they want to do.
On the other hand, I am suspicious of longer term motives, that may reduce gold making in game (or limit it to boosters in elite content) thus restricting the options of how players can afford to pay to access the game.
The game is expensive enough, given that we need to purchase all new content and a subscription to ‘rent’ everything. 
If the sub lapses - the player is back on the same footing as someone who has never played it.