Two points:

1) Alternate accounts are suspect to manipulation (anyone can create an account claiming anything), and as such what they say carries little weight. The cohesive post will have the added weight that the submissions will be verified as being written by actual female Less Wrongers, and not sock puppets with 0 karma. Also, some posters might be ok having their name associated at the level of "I wrote A submission" versus "I wrote THIS submission."

2) If you post on your own, rather than as a group, you will still run into the difficulty of being overpowered by the amount of male voices, so either few will hear you, or you'll be one against many, or you'll be taken as "single anecdote/ feminazi" rather than "The Women of Less Wrong"

That seems like enough of a trivial inconvenience to deter a lot of people, even if it was being actively encouraged in some context similar to this one. Sending a PM to Daenerys seems much less inconvenient, if more work for her.