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

Read also:

• How Many Burgers Are Too Many Burgers? Here's What Health Experts Advise. - HuffPost
• The administration’s anti-consensus Mars plan will fail - SpaceNews
• If women aren't shallow, why do most tall, good-looking men have girlfriends?
• How scientists discovered 200-million-year-old species thought to be extinct - MSN
• Slash your stress by 65% — and in just 8 minutes — with this dreamy fix to ‘calm your brain,’ neurologist says - New York Post
• Astronomers are stunned after the quiet development of the largest telescope ever built in China. - Farmingdale Observer
• What was your biggest culture shock going to Europe?
• What thing happened to you as a child that you haven’t let go of to this day?
• Why do the Republican city officials at Springfield Ohio continue to deny that immigrants are eating pets to sabotage the Trump campaign, even though immigrant pet-eating is now widely believed to be true?
• Harvey Weinstein Says He Has ‘Regrets’ and ‘Acted Immorally’ Ahead of New York Retrial Verdict: ‘But Never Illegal, Never Criminal’ - Variety
• Why do you think most harem anime and manga have lame male protagonists that would be considered losers and pathetic by most people?