Because Bungie---as they demonstrated in stamping out the "Loot Cave" and the Temple of Crota/Nexus strik exploits----is always going to keep a tight rein on the number of legendary items you will encounter out in the game world. As a solo player, my access to those game activities that will award you with them directly is very limited. So I don't want my "income streams" of Legendary gear and AS/AE to MIX. Because Bungie is NEVER going to start handing out Purple engrams for completing public events. Until I've completed my arsenal, the lengendary gear that I get from levelling up my Vanguard rank and Cryptarch will be going to EQUIP my characters, and not broken down for shards. So until I can some how find a way to start raiding, my current source of shards is BY FAR my most reliable means of acquiring them...and I don't want that slowed becauuse Bungie doesn't want the game awash in legendary gear or the shards that come from breaking them down