That would be completely contrary to their purpose (Destiny)

by Speedracer513 , Dallas, Texas, Wednesday, February 18, 2015, 07:36 (3820 days ago) @ TheeChaos

Right,

But arent the ascendant materials intended for the Raid gear of VOG? And they are drops in the nightfall.

The ascendant materials were (and still are) for all legendary gear (except for Crota's End raid gear of course). Bungie's stated purpose in introducing radiant materials this time was because they were finding that a lot of players were holding off on upgrading their normal (non-VoG) armor because they didn't want to spend their ascendant shards on the non-raid gear. But that was causing people to stay level 26/27 for a long time instead of spending the shards to level up to 28/29, making it harder for them to run VoG and have chances at that gear. Bungie wanted to encourage players to go ahead and spend their ascendant shards on the vanguard legendary armor instead of hoarding them for if/when they got raid gear, so they introduced radiant shards as the exclusive upgrade material for (new) raid gear.

However, to some extent at least, this will probably be moot going forward since Luke Smith said recently that "mistakes were made" with The Dark Below and specifically mentioned the way they implemented radiant materials as one of the mistakes they recognize and will not repeat.