Why is Abyssal Scepter still going to be an aura item? Why not make it apply an MR debuff?

The thing I've always hated about Abyssal Scepter is that long-range mages can't get it because the aura will be wasted. So why is it staying as an aura item in the upcoming rework?

Why not change it so that dealing magic spell damage reduces the target's MR by flat amounts instead? Kinda like Fiddlesticks' current passive.