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

Read also:

• What is the STAR interview method?
• If you cloned 12 Michael Jordan's and 12 LeBron James' and had Team Jordan vs. James, which team would win the most games?
• Why is there a "double standard" applied to sex between a dog and a human? Why is it that to many who are at least mildly okay with bestiality, a WOMAN having sex with a male dog is fine, but a guy with a female dog is not?
• Can you share any "backstage pass" experiences you have had at concerts?
• Can you share a picture of your favorite outfit and explain why you love it?
• What is an easy way to get your driver's license?
• While wearing high heels and walking heel to toe, when the toe box hit the floor there is a noise. How do I keep the noise just for the heel?
• Why is the world male-dominated?
• When a black man and a white woman have a child, does the child become white? If a white man and a black woman have a child, does the child become black?
• What are your thoughts on Italian nationalist poet Gabriele D'Annunzio, who was the subject of the documentary "Fiume o morte!"?
• Are INFJs essentially the most introverted type?
• What can I say to a scammer who thinks he loves me, but I don't want to be scammed?
• In Italy, how do people greet each other when they meet for the first time (e.g., on the street)? What's a good response to that greeting if you're not from Italy or don't speak Italian fluently yet?
• Summer Game Fest Viewership Jumps 89% to Record 50 Million Livestreams - Variety
• Why do females hate MGTOW so much?