Some times I feel most would want that. Cassandra seems to appeal lesbian woman far more then Sera, while Sera herself, is more approachable and feminine in her looks, wich the straight guys will obviously like more. Obviously, I'm not saying this goes for everyone.
I just wonder how many people romance Cassandra for genuine interest compared to those who only romance her because of a lack of better options.
I am a straight woman, but not averse to romancing a woman in these games if I like her enough. Cassandra and Dorian are the only ones I have any interest in romancing in DAI. If I make a guy, I'm going to romance Dorian. For that reason I would like Cassandra to have been a f/f romance option, but it wasn't to be. In fact, Cassandra is my favorite female follower in all of DAI. I'm not one of those players that tries everything just to try it, I do have to actually be interested in the character in some capacity in order to go forward.
I've seen this idea that Josie's romance was made for 'women playing men' a few times on this website. I have no idea how anyone is coming to this conclusion. First it always seems like more people romance her with a female over male (based on various polls I've seen at least). Sure, women like her and her romance but they tend to be gay/bi and romance her with a woman. I can't say I've seen many straight women talking about playing her romance with a guy.
I find this assertion annoying -- not you, the idea you're referencing -- and think it is a disservice to straight men. There are plenty of straight guys who like romance and mushy stuff, just look at all of the romances, love poems, love songs, etc. that have been written by straight men throughout history.
However, I will say that I think the only downside to the Josephine and Cassandra selection for men is that both of their romances are heavy on the romance, so I don't think there is a decent variety in that sense. Sure, Cassandra and Josephine are totally different in terms of personality and appearance, but I think the flavor of the romance is somewhat similar. If you look at the difference between Leliana and Morrigan, or Isabela and Merrill, I think there was a stronger sense of variety.