Especially without an autobid there is a need to be somewhat active. A team you are playing could have purchased a player, there's forums and a lot of other things to get involved with. This game is a living entity.
I'm not saying you should trick people per say, just that giving people a reason to want simply sign in once a day wouldn't be excessive.
I completely disagree with the idea that people aren't interested in online basketball sims, Franchise modes are big in the 2k realm... and although the approach is different I think BB if it were more engaging could attract a wide audience without the need of a complete overhaul (outside of the potential app of course).