Why do programmers choose to write their own code instead of using code that is already available online?

Read also:

• What was your best unexpected reunion with your childhood best friend?
• When do you start "growing old"?
• Can trans people tell me what the criteria for a woman is excluding self identification (facts do not rely on self belief)?
• Where are the big girls? This is the first time I've seen a bigger lady boy and that's awesome .. you should post more of them here, nothing wrong with a thick black lady
• How can someone feel more FTM when AMAB?
• Does Taylor Swift actually play the guitar, or is it a prop?
• Scientists stunned as cameras capture footage of 200-million-year-old creature once thought extinct: 'The whole team was euphoric' - Yahoo
• At what point does trespassing become self defense? What are the necessary conditions for this line to be crossed from trespassing to self defense?
• Why was the rock band Kiss so successful?
• Is it possible to become homeless after being released from jail or prison in the United States?
• Do you think there will ever be a movie that features a line such as “You graduated at the top of your class in liberal arts, we need your help”?