I expect Bungie doesn't want to support prior versions of Destiny forever. They have seen how the servers that support other games have to be around for years after the game release. This is an expense they likely want to avoid. If Destiny is on a 10 year plan as I have seen mentioned and each year they will come out with a significant change like TTK, imagine what they would need in year 7 for example. They would need separate server farms to support the prior 6 years of Destiny. This would be a huge ongoing expense which doesn't generate any income. Unfortunately anyone who doesn't buy the new version will be a victim of it.