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

Read also:

• Breast cancer makes Hull man 'feel like an imposter' - BBC
• Solar Orbiter gets world-first views of the Sun’s poles - European Space Agency
• Do older women know what they want?
• Are democrats eating crow?
• A Korean Stuido made Stellar Blade and Japanese stuido is remastering Lollipop Chainsaw. So why are western developers so aginst to cenvtunal female beauty?
• The Labour Party wants to put the Winter fuel allowance and the £800,000 of gifts received by ministers behind us. Is this a real option for the people who will suffer as our new masters unapologeticly feast on freebies?
• Can it be true that people know your name, not your story, they’ve heard what you’ve done, but not what you’ve been through, so take their opinions of you with a grain of salt?
• Is there a stereotype that South Indians are physically strong and muscular compared to other regions of India?
• What do flat Earthers think causes the "magical downward force"?
• What is the nastiest thing you had your wife do and she loved it?
• Does the West have a defense against China's PL17 air-air missile?
• Is it safe to say that China is at least 30 years ahead of India?