Teenagers to not finish high school in a conventional environment

What causes teenagers to not finish high school in a conventional environment? (Conventional environment means physically attending a high school building versus nonconventional environment would be homeschooling, earning a GED/HiSet, zooming or online learning, so this topic can focus on things like having to work or being bullied or can focus on causes for homeschooling or earning a GED/HiSet instead of a high school diploma).