I often refer to my podcast, , as "hipster homeschooling," though that's not entirely accurate. Sure, I'm a hipster by trade, and have been for almost three decades. But I'm not purely homeschooling my son Elijah. Neither he nor I would survive being at home together all the time. Also, the public school near us does a decent job, so pure homeschooling isn't necessary.
In general, people homeschool because the schools aren't religious enough, aren't nurturing enough, or, in the case of a friend of Elijah's, they're just too advanced for the curriculum. Elijah, while really smart, is also a little lazy, so an "advanced" curriculum beyond what the schools offer would be met with resistance from him. And, let's face it, I'm not qualified to teach him trigonometry, Spanish, theoretical physics, or anything much more than how to read a novel and complain about it on Twitter.
The schools do the specialized subjects well enough. He's learning math, languages, map-reading, Excel, and all the other stuff I don't want to bother teaching him. However, it's not sufficient. Extra Credit is like an extended field trip, where I, as a parent, fill in the intangibles that the schools leave hanging.