Demons are destructive- the don't have the demeanor (demoner?) to to sit there and actually design and carefully craft something as intricate as a Clockwork Horror.
I don't know. I'd see one as the incarnation of mad science, designing monstrosities based on instinct, his laboratories filled with living creatures being experimented upon. He doesn't have a list of formulas of what works, he just tries new things until something works. He creates out of the Spark of madness - he'll add claws to this human slave, put a demon's brain and an orc's beating heart into this golem, weld together these weapons and spikes until he's created an engine of destruction, mix together toxins and acidic blood and alchemical potions until he stumbles upon an elixir of pure madness...
... and something will work. And some will fail, and melt into steaming piles of goo, or just die or go inert, but
other experiments will reveal horrors beyond imagining.
In a way, I can almost see it like how Ork Technology works in Warhammer 40K. It
shouldn't work, essentially - but it does, because they believe in it, and the entire race is faintly psychic. "Red ones go fasta'" not because putting red paint on a trukk actually makes it faster, but just because that's how
they think it works.
I can see the same thing here. No rational mind would consider the clockwork horrors to work the way they do. The ability to split and divide and yet each copy is the
exact same size as the first one? That's shouldn't be possible. It's a small sliver of reflection of the infinite impossibility of the Abyss itself. The key to the Abyss is this - it is a reflection of every possible nightmare, every possible horror. And so here we have a chaos machine of destruction.
Just like there are demons that are distorted versions of men, and beasts, and the land itself, so too must there be demonic reflections of the most nightmarish possibilities of technology and contructs and logic. The clockwork horror - and its creator, the ultimate mad scientist, who feverishly churns out new impossible monstrosities from his bubbling laboratories deep in the Abyss - are perfectly at home in a realm that, somewhere in it, has the worst reflection of
absolutely everything.