There are so many male rogue Droods seen or mentioned in the series, and so little reference to female rogues, that something must have been eliminating the latter systematically. The Heart altered the Droods' genetic code so they'd always produce twins, ensuring itself a steady supply of infant sacrifices. For male Droods, fear of being found by their family meant the rogues could be counted upon to keep moving and/or isolate themselves emotionally; therefore, the Heart didn't expect any of them to settle down with a woman long enough to notice they were only siring twins. A female rogue, however, couldn't possibly overlook it if she kept giving birth to twins, which might lead to her asking awkward questions about why it was happening and whether other Droods did the same. To guard its hidden agenda, the Heart covertly kept track of the rogues' torcs (without telling the family it had that ability), then de-activated any female rogues' armor via long-distance remote control at the first opportunity to get the wearers killed.
- Going off that, the Heart pushed to get rid of Melanie Blaze. It's not as if the Heart hasn't gotten rid of people before, and given that she's an elf, with attendant spidey-senses and special pride in her children, and a non-Drood who wasn't raised to trust the Heart implicitly, it must have been hard to snow her about what happened with her first set of twins. Therefore the Heart considered her too risky to keep around and shuffled her off the board ASAP.
- This may also be part of the reason the family culture is so hard on non-Drood spouses (apart from making sure they can take it). The Heart took an interest in making it that way. After all, someone from outside the family might have taken an inconvenient interest in pre-natal care, maybe wanted the baby to be born somewhere outside the Hall, whereas a Drood would just let the Hall doctors take care of it. They might even have been able to figure out, magically or otherwise, that there were supposed to be twins on the way, and then the Droods in the know would have to figure out a coverup when only one baby arrived. Safer for the Heart to keep everything in the family, or strictly enforce conformity on those who marry in if they absolutely couldn't be frightened off.
