It's not that simple.
No-one believes they can achieve happiness without some means to do so. The internet is the perfect place to hide from other people, and books help as well. Happiness can be obtained without other people through appriciation of art, nature, and many other things. The sadness which you describe only lasts until you develop a tolerance to being starved of conversation, and can stop judging yourself with others as a point of perspective all the time. It takes years, and it's all but impossible to eliminate all contact with the outside world, but it's something that's possible to get used to.
Fear of rejection and betrayal isn't the only reason someone might reject friendship. Constant conversation brings your mind to the outside, where it can be changed without your knowledge, and where you can't see your own thoughts in the same way, since everything is spoken before you really realize it. When you hide inside yourself, you get brilliant insights from the recursive thoughts that make up your self, and everything is seen differently. Your mind becomes far more tangible. You can be free of cultural identity, have time to develop your own beliefs, and develop your personal identity free of influence. The fewer groups that you can really consider yourself a part of, the more of an individual you are.
It's a different sort of existance, but not one that should be discarded with as little thought as that. Personally, it's not the way I want to live all my life, but this lifestyle has let me come close to understanding who I am, the nature of reality, and my own mind. It's given me an appriciation for the little interactions you have with people, because when you hardly get any, a few words can mean a lot.
Really though, don't judge. People should be able to live how they choose, and it's annoying when someone tells you that you're living the wrong way.
