Because it's designed to allow you to level up favourite weapons instead of being forced to swap them for something else.
I see. So if you had a pulse rifle at say 260 attack and a scout rifle at 280 but you don't like using scout rifles, you could infuse the pulse rifle with the scout rifle? Does it depend on attack level rather than the XP level required to use it?
But why isn't it working for my exotic then? I have one at 280 (from blueprint) and one at 290 (from engram). I tried infusing the 280 one with the 290 one but it still didn't like it.
done two rift matches for the daily pvp and got nothing for it.

