Because they *do* deal with the real world, and people every day. Moreso than they'd get in a school environment.
Also - my oldest is special needs, he WAS in public school, more than one, and they failed him. I know based on my daughters personality, she would end up having a hard time in a classroom, she's just not wired to sit like that all day.
Then, you add in my 24 weeker, he can't even go to mcdonalds with out landing in the hospital during flu/cold season, because he's so immune compromised, I could not imagine sending him to preschool or kindergarten when he'd end up missing out so much on his education because of being constantly sick and in the hospital. He gets sick enough with minimal exposure and us trying to protect him during the fall/early spring flu/cold season here.
At that point, I'm already commited to homeschooling them and love the flexibility, when it's hot in texas, we do more schooling (same when it's cold.) during the off season when it's not too hot or too cold, we do a lot of outdoor activities, events, museums, field trips and adventures they couldn't do if they were in public school.
I always find it interesting, that one of the main points is social interaction, but between 4h, and many of the other things the kids are involved in, they learn far more about dealing with the real world.
For example, my daughter had to talk to the constable, justice of the peace, and sheriffs office about the dogs who were killing her chickens.
Her dad also just went through this incredibly challenging process to get her a business license (in his name until he can transfer it to her when she turns 18, if she still wants to do it.) because she wants to start her own business and has the skillset already to start the process of doing it. At 7. If you ask her if she wants to go to public school, the first thing she will tell you is "no thanks, I won't have time to do anything else I want to do."
I guess I have a different take on it - because my kid can go to community college locally, at 15-16 if she wants, and take advanced classes and it counts for college towards her BA. That's her goal actually. She wants to graduate high school as early as possible, get her BA, and do her dog business. With the amount of socializing she has to do, she's getting an education she can't get anywhere else.
She has to log work hours for her dogs, keep records, and she will need to study all the information to get her PI license at 18 to take the business over from her dad if she's still wanting to work with dogs in a few years.
She meets all these people her dad's non-profit business thing does, she's going to a class with mike suttle (they use chickens and clicker train chickens) that her dad setup and arranged for law enforcement and dog handlers.
She'd never get to do these things otherwise.
Also - every homeschooled kid my husband knew growing up, became a doctor, or something of that caliber. So, it definitely won't hold them back in life if they don't let it.
As to languages, the program we use, teaches multiple languages (my husband is fluent in spanish, too.) and has an advanced math and science program when they hit high school....
I'm not really too concerned, if they want advanced classes, there's ways to get them.
And final point, my kid knows more about the world than most kids, she actually helped deliver her little brother in the hosptial with the doctor supervising.