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

Read also:

• Is the water safe to drink in England like here in America or is it necessary to bring tablets to prevent any cholera when in London?
• Have you ever been physically attacked by a demon?
• They Were 8,000-Pound Sloths With Claws and Armor – Then Humans Showed Up - SciTechDaily
• Is It Finally a Buyer’s Market in Housing? - A Wealth of Common Sense
• Mets place Mark Vientos on 10-day IL, option Max Kranick in flurry of roster moves - SNY
• Are there girls here who like group sex?
• Why are white women so overly emotional?
• Tom Aspinall wishes Jon Jones well in retirement, declares himself ‘undisputed’ UFC champion - MMA Fighting
• Is 1500 calories enough for a 5’3 15-year-old who is non-active?
• Why do some men love sucking cocks?
• Walking This Many Steps Per Day Can Cut Your Risk Of Early Death - HuffPost
• Is it better for 2nd generation Western Muslims to marry someone from their parents' country or a western Muslim who was born and raised in the West?
• Sophia Bush Says She Endured “Every Kind of Abuse” on Show Due to Older Man - The Hollywood Reporter