If the followees were listed in order of when they last logged on, it would show you the online ones first (in order of logging on, last to first) and then all of those who are no longer online, in order of when they last logged on. That shows me which of my followees are active on here at all, meaning that even if someone is not online right now, if I can easily see, from their placement in my followees' list, that they were online recently (without having to go through every person's individual profile to find out when they were on) then I might choose to interact with someone who is not online right at this very minute, but was, five minutes before I came online.