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

Read also:

• How should I go about convincing my mother that my foreign online boyfriend isn't out to get my holes or scam me?
• Why do so many guys love anime girls?
• Why does my narcissistic ex told me that he f*cked and sleep with other woman and then at the end says that it also happened because of me?
• Why do I like to eat my own cum?
• Have you ever gone to a porn theater with your wife?
• How strict are your parents?
• Person infectious with measles traveled through Sky Harbor, health officials say - ABC15 Arizona
• How do I convince my husband that a threesome is okay?
• Why don’t the little sugar breeches gun owners understand that life isn’t all sunshine and rainbows?
• How do you fight the push and pull (manipulation) tactic if you want to win him?
• One day, I happened to walk past where my crush was with friends. Then all of a sudden they start laughing, and someone maybe him, goes "freaking (my name) with her freaking hair!" Can anyone offer insights into this? We're in middle school.
• Who are some good social skills therapists in Pompano Beach, Florida?
• Are you able to lie, even though you have Aspergers?
• Why are many women so drawn or attracted to men that have been or are currently in prison and men that are involved in street life/illegal activities?