Why do christians fornicate despite their beliefs?

I'm a virgin religious muslim I have never fornicated and I will never fornicate just because it's sin but I wonder Why do Christians fornicate? and yes some muslims do fornicate but not as much as Christians do and As far as I know Adultery is one of the biggest sins in christianity Christians know it's a big sin they're aware of it They know they will burn in hell for it but they don't care just why? Why Christians fornicate despite their beliefs?

Why do christians fornicate despite their beliefs?
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