Because the innate human desire to be liked and the moral solitude that forces most people to be nice/polite to someones face overrules the true hate they have for you and they can't bring themselves to be true assholes/bitches to your face so they bring out the "lets stay friends" line and then when you are not around that issues isn't there caue you aren't and their true hate for you comes out.
Why do people have the idea that all homeschooled people are dumb and socially inept?
Because they think that since they spend their schooltime at home, they never meet or interact with other people. Also, the assumption is often that you're homeschooled because you need special help from your parents. (disclaimer: i don't agree with that, but it's what people think)
Why do so many people just midlessly follow trends because it's cool?
Yes most people do follow trends just to make themself Feel better about themselfs or to make them think that they are fitting in Just like making fun of other people they do it so that they feel better about their own faults and too make them selfs feel better...