Why do refurbished phones have 3 months warranty or, no warranty?

Hi everyone! I am planning to buy a smartphone, but I don't know whether I should buy a refurbished phone or not. I checked many websites and most of them say that their refurbished phones function like "NEW", but they give only "3 month" warranty. If refurbished phone's performance is SAME as the Brand new phones, then why they do Not give 1 year warranty? I am confused !

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