I think this is the case if the mission fuel requirements are too high (if they want to get to a higher orbit for example), then they won't have enough fuel to

I think this is the case if the mission fuel requirements are too high (if they want to get to a higher orbit for example), then they won't have enough fuel to do the correct burns to land, even on a drone ship. Notice that they're not even including grid fins or landing legs to minimize weight.