The rumor inside the rumor is that the original story was actually scrapped because it was deemed too complex for the Teen audience they wanted to attract. The complexity of the original story and the trading / gambling aspects would have meant a mature rating and therefore limited the potential audience. See? Simple Story + Simple Mechanics + Kids = Profit.

Later

This is it, the inside story we've been waiting for since launch. [u]Highlights:[/u] - story reboot started summer of 2013 - Frankenstein story - cut content, not just from vanilla Destiny but also from The Taken King - difficult to use development tools slowing Bungie down - Activision has another studio helping Bungie make content - Bungie thought the metacritic score would be 90 - Diablo III devs brought in to talk Bungie out of RNG (I always say RNG is the worst way to reward players, and that's because it's true.) The article is phenomenal. I could read a whole book on Destiny's botched launch.