I used to ask the same question ... "I already got scars there is no point of stopping.. there is no one who gives a damn about me so no possibility of anyone finding out and getting 'hurt'... infection/accidents arent a big issue idc if i die anyway.." Over the years I've come up with an answer of my own
1 - the obvious one - it leaves really bad scarring. annoying if u cant wear shorts/shirt/uniforms/performance dress code etc
2 - Bad coping mechanism, like alcohol - 'well if drinking makes you happy whats wrong with drinking' Because with both drinking and SI you don't address the actual problems, so it grows and grows. SI made me feel better from pain but never truly "happy", and you end up just sit there watching your life slip away and go to waste.