Circumstances often make boarding school the most logical choice.
Many schools terminate at grade 8 requiring students to find a new school to attend for high school. If the commute is too long & stressful to any new school, then boarding school becomes an alternative to investigate.
Sometimes parents work or are stationed in dangerous locations abroad.
Sometimes parents work schedules involve frequent overnight travel and long hours that make daily parenting challenging.
Some kids just need to be in a school environment that can match their drive & intellgence.
Circumstances vary as do families.