Before, there was the excitement about living in a new country, coupled with the benevolence you feel towards a people you don't completely understand. You give them the benefit of the doubt. They might seem a little quirky and weird, and you might not understand all they're saying, but they smile at you and they're interesting. Plus, the sun is shining and someone is ironing your laundry at the house, and that someone is not you.
Then you return "home", and you feel like you understand everyone far too well, and you don't like what you think you know about their psyche. They're all too shallow, too pampered, too full of their First World Problems, you think, and there can't possibly be anything in it for you by getting to know them. You pine for the friends you left behind in the country you left behind, and nothing seems like it will ever be quite so fascinating and exciting again in your life as it once was.
The reason it was fascinating and exciting was mostly because it was so unpredictable. You didn't know anybody when you first arrived in your last place, and invariably you started meeting new people, whether you wanted to or not. You couldn't be picky, so you met people from the most diverse backgrounds (also helped by the fact that most expat communities are, by definition, pretty diverse affairs).
Now, on the other end of the journey, everything is very predictable. You know where to buy your groceries because you've lived here before. Or, this being America, you don't have to have lived in the exact place before to still know pretty much everything there is to know, because it is the same mostly everywhere.You know that you'll have to start pumping your own gas again, or if you've temporarily forgotten, you'll re-learn it quickly after standing forlornly at the gas station with no attendant instantly materializing by your side. If you're moving back to the place you came from, you already have friends, your children already know the school, and nothing has changed but you.
Of course it's not really like this. This is just the silent conversation you have in your head. What it really is like is the same as everywhere: You have to allow some time to settle in. Which will be made much easier if, in the words of I Was An Expat Wife (aka Maria Foley), you treat your home country like any other expat location - with curiosity, an open mind and heart, and a willingness to adapt.
You have to overcome your own snobbishness to realize there are wonderful people everywhere in the world, and only then can you form new friendships and move on with your life. You might play bocce and beer pong with your new friends instead of climbing Mount Kilimanjaro, but it'll be fun nonetheless.