Hextech Sweeper: Why armor?

I complain about this basically every time I have to buy sweeper against a primarily magic damage team on the howling abyss and it got me wondering how many of my fellow players think its a problem, too. I searched for threads about hextech sweeper and all I found was one made 2 years ago with 0 comments so I think its time to invite this discussion again.

Why does on Howling Abyss give armor AND reveal traps? The only AD trap in the entire game was added with Jhin, YEARS after the item was first introduced to the Abyss. In literally every other situation where you'd want to buy Hextech Sweeper you'd also want magic resist and armor would be a useless dump stat.

In consideration of MR and trap detection being too strong on a single item we could switch the build up such that the final stats include Base Health Regen instead of either armor or MR. This give us sustain to deal with traps or at least a stat that is good on every champion regardless, removes the bad feeling of paying for armor when we frequently don't need it and avoids the issue of being TOO good against trap characters, since we don't want a single item to totally negate them, just make the game playable against them on the Abyss.

A second option that I personally think is too strong is to make it a third option to build out of Aegis and have it give the aura and retain its active/passive sweeping effect.