Mostly politics.
She can’t work there as a woman, they would have to give a different job. I think it would be rather easy to fix and they just haven’t yet because the most important one of them didn’t know.
Know that he does I expect someone to bring it up soon. There really isn’t a reason to hide it anymore like you said, I think it just wasn’t super important. He kisses her as a boy anyway  ╮( ̄▽ ̄)╭                                            
                                                I think it still has its uses as a political cover given that it's not really talked about.
Even the innermost circle doesn't talk about it themselves unless absolutely necessary.
For instance, i think it keeps the corrupted parents/empire(?) from finding out the scheme's up, postponing  any consequential actions from their part
It also prevents people from trying to find out exactly who she is, w/c can be problematic if the investigation caught them unawares / twists the truth/ used as leverage if someone else beat them to it                                            

		
why is she still pretending to be a man when all the ”important” people already know she’s a woman?? or do i just not remember why