I don't understand why people are busy elsewhere but their skype's condition shows they are is online.

These days using skype, Recently I have noticed found that many people were are often online, almost all day. Is it a habit, ? or do they forget to change to offline, or away or do not disturb? In China, this phenomenon also exists because the chatting application has a reward, which is the longer you are online, the higher your level you have. The user can get earn some privileges from the higher level. I don't know whether skype has this priviliege or not. I am confused about this that and I don't know when it's a good the better time to chat with others. I often ask my friend if he is busy or not. Do you meet have this problem?