imo the biggest driver for the servers being dead is that dm is really only playable with 6+ people. There aren't any systems in place to deal with a server being not-full, so trying to start a dm server by yourself is actually a bit of work and the incentive to join a low population dm server is really low. I think that combination of factors makes it not worthwhile to try to get a dm server going when you're outside of the dm prime time in NA
I honestly don't know if there's a good fix for this, but at the very least having no afk timer for a server with less than 4 or 5 people would remove the hurdle of needing to be tabbed in to try to get a server going