For someone who describes themselves as "extremely bright" you appear not to be capable of thinking "outside the box". Children are home schooled for so many varied reasons. You idea of keeping a child at home and "inflicting" "your idea of what they should learn and what they should become " is laughable.
How on earth have you formed such a limited view??
OK - Some good reasons why families home school : We travel a lot and it suits us to educate our children with us on the road so we remain together as a family. I don't consider myself "selfish".
Others we know home school because they are geographically isolated - the nearest school many hours away. Two of my daughters friends live on boats and have done so since they were babies and are part of the cruising community. Another lives in Thailand where her parents have set up a refuge for Karen women & children. Dd's godmother home schools her autistic son with great results - he, like you, is "very bright".
We have 2 friends who are gymnasts and they flexi school as they do 28 hrs in the gym each week - they do 2.5 hrs of contact school a day.
We have met home edders that just didn't thrive at school for one reason or another. Bullying an issue in one case that wasn't resolved and led to great unhappiness.
My dds belong to a teenage home school forum and there are kids they have met on line who are not well enough to attend school, one with social anxiety and another with an auto immune issue.
We meet lots of other home edders on the road and I am yet to meet the parent you describe. I am so grateful I have the opportunity to spend endless unhurried hours with my dds who I would describe as such open, big hearted, endlessly curious .....and did I mention "bright" souls.