This is really not enough to go on to draw any sort of conclusion. As has been said before, those stats come from Steam specifically which only tracks which characters were selected on some games. This provides an unrepresentative sample of people who play CoG games because, to my mind, Steam has a more homogenous playe base as far as IF games go. Not to mention the small sample of games selected.
It is interesting to think about though. I think the only way to figure out which ROs are the most popular would be to administer some sort of survey asking participnats what their gender and sexuality is, as well as what gender character they prefer to romance in the games. The most consistent results night come from the forum here, but this would also exclude casual players who are only aware of CoG games from other store fronts. It is entirely likely that results would differ significantly based on what store the sample was drawn from.
Anyway, it would be very difficult to say what ROs are most popular and why without knowing who is selecting them and why, let alone how many actually are.