Galvanic Corrosion

Why do we offer zinc plated steel hardware and not copper or stainless steel?
Two words - galvanic corrosion.
There are other reasons, but the main reason has to do with incompatibilities between differing metals.
Why's this important? Without going into a lot of chemistry, physics, and metallurgy, let's just say it has to do with the transfer of electrons. 

On a basic level, when you put two metals together, you get a difference in potential. Electrons flow. Guess what that is commonly called.
Yes. A battery!
"Oh, but wait" you say... "A battery also has electrolyte".
You are correct. To make the needed electrolyte for our battery, we can use two simple ingredients.
Water and oxygen.
Oxygen is in the air obviously, and unless you are living in outer-space, there is water in the air as well. It's called humidity.

When the electrons move from one metal to the other, metal ions are transferred as well. Over time, the metal surface goes away, ion by ion. 
And now that there is less metal in contact, there is higher resistance. Higher resistance creates all sorts of bad issues.

Now that you have an overly simplified description of what's going on, we will show how to mitigate it as much as possible and limit the corrosion in future articles.

Referring to the chart here:
https://structx.com/Material_Properties_001.html