Why do bombers only have elemental defense?

All 4 existing bomber armors (Bombastic, Volcanic, Mad Bomber, and even the Shadow Lairs' Mercurial Demo) only have elemental defense. No piercing or shadow in there.
This isn't a rant thread, I just want to know what made the devs decide that bombers only need to be protected from elemental attacks and nothing else.

And it's called Mercurial Set (the one craft from Quicksilver Set).
I think somehow movement speed bonus has been classified under Bomber's UV. So if you can always mix Mercurial and Mercurial Demo set to get benefit of both elemental and piercing resistance.

Mercurial Demo Suit offers elemental defense and a bomber bonus. Mercurial Mail offers piercing protection but no bomb bonuses. I think that you're getting them confused.

Hrm? Mercurial Set isn't a bomber's set. Case in point, it has no elemental defense... or bomb bonuses.
The reason they all have elemental defense is because explosions are elemental damage, as a blast block demonstrates.

People who play SK think Movement Bonus is not a Bomber's trait.
The folks at OOO probably think the other way.
There is no confusion. It's intentional.

Next thing someone will say is that Deadshot is a gunner set.

Move speed is not a bomber trait. Even if it was, the difference is negligible, move bonuses are so low it's not even worth mentioning.

I'm surprised that none of the sets have a trait to reduce bomb fuse time. (That is, from the time you lay down the bomb to the time the bomb blows up.)
Mercurial Demo set should have this trait to make it useful. Leave the movement bonus to Mercurial set.
I want a Skelly/Demo Suit Fusion for Shadow Defence & a Pierce-Resistant Demo Suit that looks like the Mercurial Demo Suit w/o the Huge Pack & more Darker!
MOAR DEMO VARIENTS!