I am curious about some people's facebook habits. I know some people who check facebook like 5 - 6 hours a day but they never post anything. I check maybe 2 hours a day and I do like to post every few weeks but never understood how someone can be on FB all the time but never post anything. Do they have low self esteem? Are they afraid something about them will come out? They trying to hide something?

and you care about it, why ?

I already said I am curious about it. If this is not something that you care for, simply ignore it.

Maybe some people just like to watch other people's business but keep their own stuff private.

I like Alt Real's comments.
every individual is different!

Alright, first hand experience here . I don't spend that much time in Facebook anymore, but used to spend around an hour a day and I barely posted anything. I would not post anything that did not need to be posted. Like I never posted a single picture or updates of what I am currently doing , what I ate or where I went for vacation. Every tag and post made in my wall needs review. If I change state to live , I would update that in profile but if I get promoted , I won't post it. The only reason I still use Facebook is because most of my friends use it and is primary messaging platform. I am not interested on every single feeds about my Facebook circle either, but it is good to know that my childhood friend got married who I hardly talk with or a friend moved close to my place e.t.c . Most of the time I spent scrolling feed would be more about to watch feeds from the pages I followed which included feeds from trolls, comedians, sports, gaming, motivational and some career related. If you follow few active pages, your Facebook feeds would usually be filled with them. Most of my friends know about this behavior, because I react to their post every time I get chance or find reasonable. If it was low esteem , I would probably pretend like I was never there and would not react on any post.

But 5-6 hours a day is too much to spend on Facebook. If they have that much time to spend on Facebook, I don't think they have time to do anything useful. So unless they want to post updates like "scrolling feeds on Facebook" , i don't think they have anything to post anyways.

Consider this..there have been incidents where people posted their vacation pictures while they were away from home along with exciting notes along the line suggesting their vacation plans only to find that their home was burglarized while they were away.