(Weapon swap) why i lost dps skill on set 2 only

Why when i try to put skill on only weapon set 2 I lost out 40 %dps. Got the same weapon in both set. as soon i click on a skill(rampage) to set it to only on set 2 lost dps.

only got 1 tree no 2 separate tree for weapon swap,rampage 73k dps set 1 only if i set it set 2 only 48k and the dps box look gray in set 2 compare to 1

Is there something I am doing wrong thx