The reason is simple if you have both you create a glitch / loop hole that players would use to get a ridiculous amount of marks / materials , which in turn would ruin the economy of the game . And if anyone says there is no economy to the game you are wrong and need to understand the structure of how a game works . But having one over the other is a choice they had to make to keep balance end of story and the way it is now is way better and to say that resources were only good to get vanguard marks so you can get easy shards just makes you sound lazy if you do your raids strikes, weekly and daily. You would have no issues getting what's ore energy! now everyone who is complaining go hit the crucible and do the strikes and stop whining! And stop finding holes in the game to make it easier . The reasons for doing this was obvious to make the game more challenging as for the fact that it's to easy to get to 30 minus having to do V.o.G.