Whoo! Double Questions!
How can dwarfs be sooo... thoughtless and end up dying from commonsense things?
Dwarven minds prioritize things differently.
"Oh, a zombie bear? Well, we should keep those socks outside safe."
How does a bronze colossus use a staircase made for dorfs?
Quantum Space compression. Everything looks about the same size, but have very different masses.
A Bronze Colossus looks like a regular old human in height, maybe a bit taller, but they have the mass of one fourth the statue of liberty.
Why are there only Bronze Colossi? Why not Iron Giants?