There are different stainless alloys with different properties used for a myriad of products, and not all are harder than all carbon steel. You may be comparing the cheapest mild hot rolled steel with a harder stainless alloy.
In the US, you can call it "stainless" if the alloy has at least 10.5% chromium. Nickel, carbon, molybdenum, manganese, copper, and even aluminum and titanium can be in stainless alloys.

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