system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is stainless steel made, and why is everything metal not made of it?

If it does not rust, then why are cars, tools, everything else that may rust not made of it? Is it a cost issue?
gpt
Stainless steel is a group of steel alloys with high chromium and low carbon.  This makes them significantly more resistant against corrosion but the low carbon content means that it's flexible and not very strong

We often use high carbon steel for items that we want to heat treat and make extremely hard.

There are other alloys that are really magnetic or not magnetic at all.

There are about a thousand alloys of steel, each excels in certain areas and is preferred for certain tasks.  With the variety of alloys out there, why pick one to use for everything rather than picking the perfect one for your application?