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

Read also:

• Senate expected to pass crypto bill without addressing Trump’s investments - AP News
• What is the recommended approach for creating a film or TV script? Should the script be written first or should the story be developed first? Why?
• ‘Wicked: For Good’ Trailer: Ariana Grande and Cynthia Erivo Put Glinda and Elphaba to the Test in Dazzling First Footage From Sequel - Variety
• Do you suck dicks with no reciprocation?
• How do you dry your hair fast?
• High-Average, Low-Slugging Hitters Are Back, and Baseball Is Better for It - Sports Illustrated
• AI Experts say that, "with the advancement of AI, humans will stop coding within a few years." How much do you think this is true?
• We’ve Found Sauropod Stomach Contents For The First Time, Revealing They Had Terrible Manners - IFLScience
• What would happen if the US government told the British government in no uncertain terms all RAF bases with USAF personnel now must follow the Constitution and us law, and if the UK tried to defy this, the US military would directly attack the UK?
• ESO Seasons of the Worm Cult Dev Q&A – ‘There’s Tons of Exciting Stuff We Haven’t Talked About That’s Coming to the Game’ - Wccftech
• Who believes that Speaker Mike Johnson will certify ‘a free and fair and legal election'? Who believes that Speaker Mike Johnson will NOT certify ‘a free and fair and legal election'? Why?