I bought this twice on my highest level characters. It's a way to quickly get rid of max gold and make room to sell additional items. It's also a quick way to transfer 75,000 gold to a lower level character.
No to mention, if you want to display it in your treasure room, you can be the envy of all who may stop by your castle.
There are several sizes of treasure piles that cost varying amounts.
This is just a way to show off how much gold you've accumulated. Some people spend a lot of time farming and reach the gold cap easily. They don't want to buy items or equipment that is going to clutter their banks/backpacks/houses/attics. Besides can you imagine how much stuff you would have to buy in order to deplete that 200,000 gold? So this is basically a way to get rid of your gold & show your status with just one item. :)
PS I do believe, though, that with the addition of Advanced Pets more people are spending their gold on morphing and hatching!
Now that the Morphing tent is drinking in my gold as fast as I can pour it, none of the expensive treasure piles are much of a temptation any more!. At 10,000 to 21,000 a pop, morphing cleans a pirate out fast.