That is because
bonus2 bAddClass,Class_All,2;
is the modifier for the Atk. It is working, it just doesn't display through your Atk stat. It doesn't function the exact same way either.
But if you want to make an item directly affect the BaseAtk there is this function:
bonus bAtkRate,n; Attack power + n% (unofficial)
But as it says in the doc/item_bonus.txt it is unofficial, so you don't see it used. I haven't used it myself but it should work.