I would never presume to know everyone's situation, but I do know people who use Facebook in similar ways. I believe, it's their way of getting attention and hoping for pity or validation or whatever.
I know someone who posts constantly. Everything she posts is either a great tragedy (a mosquito bite on her foot - oh, no! How will she ever be able to put on shoes and be a waitress for 6 hours?) or the greatest thing ever (Look, someone brought me McDonald's! I'm the luckiest girl in the world!!!) I couldn't take it. I had to unfollow her.
I do have another FB friend who is in the military. She posts all the time, but she doesn't post anything similar to what you are saying. She posts because she is away from all her friends and is often lonely. She's actually quite mature about it and has made friends there. Still, who can blame her for wanting to stay connected.
I honestly believe that some people are just insecure or lonely and hoping that their FB friends will write things to make them feel better. Honestly, I pity the first person I mentioned, and I pity many other people. Facebook has it's place, but if you're using FB in order to feel validated, I really do feel sorry for you.